NOTE: THIS DOCUMENT WAS CREATED VIA OPTICAL CHARACTER RECOGNITION (OCR) TECHNOLOGY, AND IS LIKELY TO CONTAIN (WHAT ARE THE EQUIVALENT OF) TYPOGRAPHICAL ERRORS. THEREFORE, IT IS STRONGLY ADVISED TO REFER TO THE ORIGINAL SCAN (SEE URL BELOW) FOR QUOTES (ESPECIALLY OF NUMBERS AND/OR FORMATTED ITEMS [E.G., TABULAR INFORMATION]). REFER TO THE DOCUMENT ONLINE AT: http://www.hear.org/articles/pdfs/mcgregor1973.pdf The Emigrant Pests By Dr. Russell C. McGregor THE EMIGRANT PESTS A Report to: Dr. Francis J. Mulhern Administrator, Animal and Plant Health Inspection Service Dr. Russell C. McGregor Consultant, 484 Kentucky Avenue, Berkeley, California 94707 and Chairman, Import Inspection Task Force Task Force Members Mr. Richard D. Butler, Planning and Evaluation Staff, APHIS Mr. Austin Fox, Farm Production Economics Division, ERS Dr. Donald Johnson, Liaison Officer, ARS - Army Dr. C. H. Kingsolver, Plant Disease Research Laboratory, ARS Dr. Bert Levy, Biometrical Services Staff, APHIS Mr. Herbert E. Pritchard, Management Improvement Division, APHIS Dr. Reece I. Sailer, Insect Identification and Beneficial Insect Introduction Institute, ARS May 1973 A report on exotic pests and diseases of plants and animals, including -- --an analysis of the threat they pose to the environment and the agriculture of the United States, --an evaluation of the inspection and quarantine programs of the U.S. Department of Agriculture, --a proposal for increasing the supply of protection on a global basis. TABLE OF CONTENTS Page 1 Introduction 11 Statement of the Problem....................................... 1 11.1 Disagreement on Objectives 11.2 Program Effectiveness 11.3 Changes in International Traffic 11. 4 Expanding Budgets 11. 5 Agency Relationships 11. 6 Baggage Inspection Standards 11. 7 Improved Detection Capability 12 Objectives..................................................... 4 13 Approach....................................................... 4 14 Procedure...................................................... 5 2___The Arrival of Immigrant Species 21 The Potential for Introduction................................. 7 22 The Pathways................................................... 8 22.1 Historical Pathways 22.2 Aircraft 22.3 Scientists as Pathways 23 Colonization and Establishment................................. 11 23.1 Food Resources and Environmental Resistance 23.2 The Sweepstakes 23.3 Genetic Barriers 24 The Record of Establishments................................... 13 25 The Hawaiian Experience........................................ 17 26 Immigrant Species as Pests..................................... 20 26.1 Predictability 26.2 Relative Importance Page 3_____Defining the Threat 31 The Threat of Invasion......................................... 26 32 The Values at Stake............................................ 30 32.1 Outlook for Social Value of the Environment 32.2 The California Model 33 The Model for Ranking Importance............................... 33 33.1 The Conceptual Design 33.2 Mathematics of the Ranking Model 33.3 Predicting Probability of Establishment 33.4 Economic Impact of Agricultural Pests 33.5 Assembling the Information 33.6 Explanation of Computer Documents 33.7 Infestation as a Poisson Process 4_____The Exotic Pests and Diseases 41 The Ranking.................................................... 54 41.1 Expected Economic Impact 41.2 Probability of Establishment 41.3 The Limits of Knowledge 41.4 Comparing the List 42 U.S. Commodities as Targets.................................... 42 42.1 Host Materials as Carriers 43 The World Distribution of Species.............................. 66 43.1 The Outlook for Introductions 5_____Programs for Foreign Protection 51 Survey of Foreign Programs..................................... 73 52 Travelers...................................................... 75 53 Program Assessment............................................. 78 54 European Experience............................................ 80 Page 60 Programs for U.S. Protection 61 History....................................................... 82 62 Federal Inspection Agencies. ................................. 87 63 Objectives and Strategy....................................... 90 64 Regulations and Procedures.................................... 92 64.1 Plant Pests and Diseases 64.2 Animal Pests and Diseases 64.3 Initiation, Modification and Termination 65 New Transportation Technology................................. 97 65.1 Containers 65.2 Ships 65.3 Ports 65.4 Planes 66 Detection Devices and Control Methods......................... 111 66.1 Present Detection Devices 66.2 Present Control Methods 66.3 The Potential of Sniffers 66.4 The Potential for Traps 66.5 The Potential for Listening and Other Devices 66.6 Remote Sensing 66.7 Control by the Irradiation of Commodities 66.8 Control by the Irradiation of Passenger Baggage 67 Sampling...................................................... 117 7 ____The Assessment of U.S. Quarantine Efforts 71 Baggage Inspection............................................ 121 72 Deterrence......... ........................................... 128 73 Quarantine Impacts............................................ 133 73.1 Trade Barriers 73.2 The Viewpoint of Carriers 73.3 Inspectors' Comments Page 74 The Assessment Dilemma........................................ 141 74.1 Indirect Assessment 74.2 Direct Assessment 75 Evaluation Techniques......................................... 149 8 Conclusions and Recommendations 81 Principles.................................................... 151 81.1 Emphasize Global Movements 81.2 Adopt Balanced Objectives 81.3 Concentrate on the Highest Risks 81.4 Reduce Biological Uncertainties 81.5 Emphasize Compliance 81.6 Encourage Private Efforts 81.7 Establish Risk Standards 81.8 Provide Evaluation 82 Strategies.................................................... 155 82.1 Develop a Source Inspection System 82.2 Revise Program Strategies 82.3 Monitor Customs Baggage Seizures 82.4 Eliminate Border Inspection of Passenger Vehicles 82.5 Regulate Germ Plasm Traffic 82.6 Develop Pan-American Quarantine 83 Operations.................................................... 163 83.1 Review and Streamline Regulations 83.2 Establish Uniform Inspection Procedures 83.3 Employ Statistical Sampling 83.4 Use the New Detection and Control Devices 83.5 Test Pathway Survival 9 Appendix (A Separate Volume) THE EMIGRANT PESTS by Dr. Russell C. McGregor OVERVIEW AND CHAPTER SUMMARIES The Phenomena I There is a continuous stream of new organisms being carried into the U.S. from overseas and establishing themselves in the North American biota. A. During the past 480 years, 1,115 new insects have become established, increasing U.S. insect fauna by 1%. B. The rate of establishment of new insect species has been relatively stable since about 1920, at 9 new insects a year. C. These 9 annual insect immigrants include 5 agricultural pests, 2 beneficial insects, and 2 insects of no importance. II There is a substantial reservoir of organisms awaiting transportation, including many that are expected to become pests upon arrival. A. There are 1,333 pests believed to be a significant threat, 22 animal diseases, 551 plant diseases and 760 insects. These are individually identified and described in the report. B. At present rates of establishment there is a known 300-year supply of insects alone that are expected to be important U.S. pests. C. There are 29 species that would attack the U.S. soybean crop, 7 of which are individually capable of causing yield loses of 10% or more. III When they are established these emigrant pests are expected to produce a wide range of economic impacts on U.S. agriculture. A. Two percent of them (25 species) may produce impacts from $401 million to $4 billion; whereas 75% of them (1,001 species) may produce impacts of less than $4 million, a thousand-fold range between classes. IV There is no objective evidence that U.S. quarantine actions are having any significant impact on this flow. That doesn't mean the program is without effect, but rather that the haphazard use of sampling during inspection and the lack of certain biological information precludes a quantified evaluation. Proposed Actions I Until such time as objective evidence of program efficacy can be provided, the continuation of some kind of quarantine effort appears prudent. II The regulation of passenger baggage by APHIS is judged unlikely to contribute to significant risk reduction and should be abandoned or substantially modified. III The regulation of agricultural cargoes has received general acceptance by the nations of the world, but existing practices should be strengthened by the implementation of the principles inherent in ASIST (Agricultural Source Inspection and Surveillance Technique. ) SUMMARY CHAPTER 1 - Introduction Doubts about the efficacy of our efforts to prevent the entry of exotic agricultural pests and diseases coupled with rising volumes of international trade and travel during a period of budget restrictions prompted Department officials to look for more efficient alternatives to the present array of quarantine program activities. A Task Force, comprised of individuals not then employed by the then Agricultural Quarantine Inspection Division of ARS and chaired by an outside consultant, was appointed to do this. The Task force was told that its objective was not primarily to evaluate and critique the current program, but rather to define and quantify, if possible, the risks from the entry of those exotic agricultural pests and diseases that are major threats to our environment and our food supplies, and to develop and analyze strategies for protection against these pests and diseases. The approach to the problem as spelled out by Drs. Ned Bayley, then Director of Science and Education, and Francis J. Mulhern, Administrator of APHIS, and the procedures followed by the Task Force are described in the closing paragraphs of Chapter 1. CHAPTER 2 - The Arrival of Immigrant Species The continental U.S. has been and is particularly prone to pest introduction. It was settled and developed agriculturally in less than 500 years. In many instances pests came along with the introduced crops and livestock species comprising the bulk of our farm output. Conservative estimates place the number of insect species in the world within a range of 2.5-5 million. Among this vast horde exist species adapted to fill any conceivable ecological niche. It is doubtful that any terrestrial animal or plant is immune from some form of insect attack. The same is true of pathogenic organisms. The fact that plants and animals are able to exist in communities pervaded by such entities is a consequence of evolutionary processes that interpose checks and balances on the disproportionate increase of any member of the ecological community. Since ecosystems evolved long before man became an important force in evolution, their stability was determined by factors of climate, geography and isolation. During the past 480 years, the geographic barriers provided by the Atlantic and Pacific Oceans have been breeched and the ecology of the Western Hemisphere changed by man's agricultural, social and industrial activities. The consequence of this has been the colonization of a succession of immigrant agricultural pests and diseases. Initially, the successful species were those associated with man, his stored products and his livestock which could survive a long sea voyage. Later, nursery stock for planting orchards was brought in accompanied by a variety of disease pathogens and insects. The new species often found previous "pest-free" crops and an environment where natural enemies were absent. Changing patterns of immigration have resulted in an influx of agricultural pests from all over the world. Since 1940, aircraft have assumed increasing importance as a pathway of entry, as they have permitted short-lived, winged hitchhikers to survive transit and escape into new geographic areas. Deliberate introduction of pests occur occasionally as a result of carelessness in scientific research. This pathway could become more important as research on genetic control increases. Following the arrival of an agricultural pest, a succession of events must transpire before the pest becomes established. These events take the form of obstacles which must be overcome--each with its own probability of occurrence. They are considered in some detail in Chapter 2, and taken together, they add up to a formidable natural barrier to successful colonizations. Despite these natural forces, a substantial number of agricultural pests and diseases have become established. For example, over 1,100 foreign species of insects and mites now call North America home. These immigrants amount to only 1 percent of the total insect and mite fauna of the Continental U.S., but the pests among them account for over two-fifths of total crop losses. The record of discovery of new insects reveals a rapid increase up to about 15 species per year in the 1910-19 decade. Since then, discoveries of new species have leveled off to a rate of around 9 species per year. The number of potentially significant variables affecting this time series makes interpretation difficult. The experience of Hawaii in attempting to keep foreign pest invaders at bay may be significant in appraising the effectiveness of quarantines. These climatically favored islands have never been connected to any continental land mass and were geographically isolated from world biota prior to the arrival of Europeans in the 18th Century. Over the past 250 years, the native fauna has been, in good part, displaced as a result of the actions of nonindigenous man. Over 1,000 species of insects and mites have been recorded as immigrant to Hawaii, and in the 1942-72 period, the rate of colonization per 1,000 square miles was 40 species, 500 times the rate for the continental U.S. This, despite a quarantine effort more intensive than that for the contiguous U.S. Conclusion: It is not the deterrent effect of quarantine inspection but rather some ecological difference that accounts for the disproportionately low immigrant fauna present in the contiguous States. A breakdown of the 1,115 immigrant insect species shows that 221 were not economically important; 404 became minor pests; 212 were important pests (but we wouldn't have expected 139 of them to be so on the basis of their performance in their native land); and 278 turned out to be beneficial (of which 126 were deliberate introductions). Manifestly, there is a high degree of unpredictability about the likelihood of exotic insects becoming pests. CHAPTER 3 - Defining the Threat There are perhaps 2,500,000 insect species not present in the U.S. About 800,000 of these have been identified and 6,000 of them are known to be damaging in foreign areas having ecological equivalents of the U.S. It may be that the low predictability for pest behavior among insects precludes compilation of a list of injurious exotic species which would provide reasonable basis for program decisions. However, since we cannot protect ourselves against everything, it is useful to have some ordering of the potential invaders that provides an opportunity to make choices, however uncertain, in the use of program resources. The Task Force identified 600 species of insects and mites that may be regarded as high risk. There are perhaps 10 times that number that may be suspect. Exclusion of all 6,000 might be desirable, but the cost would be prohibitive, if it could be done at all. While the probability of establishment differs among species of emigrants, taken as a whole the probability of any given species becoming established in a given year is very low. Experience suggests it may be on the order of 0.04 to 0.22 percent. The situation with respect to plant pathogens is quite similar, with 551 species believed to pose significant risks to our agriculture from a list of 2,000 potentially bad actors. With increasing concern about environmental quality, the relationship between environmental and aesthetic values and exotic pests and diseases is one that deserves more attention than it has received. The impacts which exotic pests may have on the environment are difficult to quantify, but that they can be serious from the standpoint of the affected public is evident from the reaction to such imports as the gypsy moth and the fire ant. New pest arrivals can also upset established methods of pest control and result in greater reliance on pesticides. Through the use of a mathematical model, the Task Force sought to identify the most serious emigrant pests (based on information provided by knowledgeable scientists) and to rank them according to the risk they posed to U.S. agriculture. The usefulness of the model is limited by the quality of the scientific judgments that constitute the greater part of the inputs, by the decision not to include social and environmental values, and by its static nature. In fact, the results of the model are best thought of as a summary of the opinions of the expert biologists on the Task Force. It would be misleading to consider those results as scientifically (i.e., experimentally) derived. Simply stated, a ranking of exotic pests emerged from a three-step procedure: 1. Estimate the probability of specific exotic pests becoming established in the U.S. 2. Evaluate the economic impact if those pests became established. 3. Multiply the results of step 1 by those of step 2 to obtain the expected economic importance of each pest. This brief outline of the concept severely understates the complexity of the formulae used to complete steps 1 and 2. These are elaborated in detail in Chapter 3. Through the use of computers the manifold computations were completed, and the desired information printed out. One of the more important outputs was a bar chart where the length of the bars represent a 75 percent confidence interval for the "Expected Economic Impact" of the pest, and with the pests listed in descending order of the upper end of the confidence interval. CHAPTER 4 - The Exotic Pests and Diseases Task Force biologists provided essential information on 1,333 exotic pests and diseases which, in their view, constituted a significant threat to the U.S. In this group were 22 animal diseases, 551 plant diseases and nematodes and 760 insects and mites. The 100 top ranking exotic pests identified by the methods described in Chapter 3 are shown on a table in Chapter 4, and the complete list of plant pests and diseases ranked in order of their Expected Economic Impact is a part of the computer printout included in the Appendix. The list of the top 100 illustrates how rapidly the EEI declines as one proceeds down the ranking: From a top of almost $4 billion, to $40 million. Given the weakness in the available information, the dollar figures should be used more as a scoring device than as a representation of true value. Twenty-five species, or 2 percent of the 1,333 agricultural pests and diseases regarded as potentially serious, had EEIs exceeding $400 million. At the other end of the highly skewed array were 1,001 species - 75 percent of the total - with EEIs of less than $4 million. Twenty-one of the top 100 species have a high probability of establishment—a mean time until first infestation of up to 3 years. This first group included 6 animal diseases, 7 plant diseases and 8 insects. Forty-three species fall in the 4 through 6 year category, while the average time of first establishment of the remaining species is more than 99 years. Here again, these findings should not be taken too literally. In assembling information on the exotic pests, Task Force biologists often found that biological knowledge of key attributes was quite limited or missing altogether. This creates a great deal of uncertainty about international movement, colonization, damage, etc., and is responsible for the wide range of EEIs observable in the printout. We should gather much more information about exotic pests, especially those at the top of the list. While the top 100 represent a "clear and present danger," it would be foolhardy to ignore classes of pests which present similar danger, even though individual members do not appear important in themselves. A comparison of the Task Force list with other lists of dangerous exotic pests disclosed a large number of differences which are not easy to reconcile. Details are presented in Chapter 4. --Major International Pest and Disease Threats --The Consequences of Introducing Exotic Pests --International Pathways of Pest and Disease Movement --The Effectiveness of Quarantine Programs --Protection as a Concept --Increasing the Future Supply of Protection --New Programs These topics served as a working outline for the final report. They also provided the framework to identify the individual tasks that needed to be done. Second, 36 separate tasks were described, assignments of personnel were made, and deadlines established.1 Each description included the title, objectives, assignment, performer, time, deadline, product, and approach. Third, a critical path flowchart was laid out illustrating the span of working time for each task and its relationship to other tasks. 2 This chart, termed a "Game Plan," also arranged the tasks according to the kinds of talents required; i.e., entomology and pathology; psychology and sociology; history, law, policy analysis; economics; engineering and transportation; statistical analysis; organization and management; synthesis and interpretation. In addition, the Game Plan called for 12 output and recommendation papers to be produced during the year-long study As expected, there were many alterations made along the way, and the deadlines required constant readjustment. Fourth, six Task Force members, knowledgeable in some aspect of the problem, were selected to assist in getting the task completed. At the first meetings the objectives, the outline of issues, the task outlines, and the Game Plan prepared by the chairman were reviewed and revised. At subsequent meetings progress was reviewed, status reports were prepared, and plans were updated and revised. Finally, the chairman prepared a draft from the papers submitted for each of the tasks. Each member of the Task Force reviewed and critiqued the draft, resulting in this final report. 1. A complete list of titles of the tasks is in Appendix 1-A. 2. A copy of the Game Plan is Appendix 1-B. TABLE 4-1 (Cont. ) Species Type Probability of Establishment EEI Mid-Point EEI Range (Plus or Minus) Confidence Interval Direct Rank 50% 90% Estimate 41 Lepidosaphes tubulorum I L 183 89 219 42 Heartwater (R. ruminantium} A H 178 50 43 Acanthostigma parasiticum P M 174 8 20 44 Sclerospora philippinensis P M 161 12 30 45 Sclerospora spontanea P M 152 7 18 46 Scolytus scolytus I L 151 423 1,045 47 Cerambyx cerod I L 151 104 258 48 Tomicus piniperda I L 137 95 235 49 Teschen disease A L 133 44 50 Maize streak virus P M 132 8 18 51 African horse sickness A H 120 30 52 Mycosphaerella sojae P M 116 8 18 53 Cerambyx scopolii I L 116 324 801 54 Rice dwarf virus P L 115 8 20 55 Septoria maydis P H 112 10 25 56 Rift valley fever A M 112 33 57 Synchytrium dolichi P H 112 10 25 58 Xanthomonas vaculorum P M 107 6 12 59 Synchytrium umbilicatum P H 104 10 23 60 Datura 437 virus P M 97 6 14 61 Corynebacterium tritici P H 92 8 20 62 Macrophoma mame P M 91 6 14 63 Lepidosaphes newsteadi I L 91 45 111 64 Dasychira pudibunda I L 87 162 399 65 Ceratitis capitata I H 84 11 29 66 Zabrus tenebrioides I L 83 44 109 67 Agrilus viridus I L 82 231 570 68 Colletotrichum zeae P M 80 8 22 69 Zadiprion vallicola I H 78 2 11 70 Operophtera brumata I L 71 35 85 71 Maize stripe virus P M 71 4 10 72 Heliothis armigera I L 67 27 67 73 lraaoderma oranarium I H 66 4 10 74 Soybeans yellows mosaic P M 65 4 8 75 Largionia vitis I L 63 25 63 76 Pythium volutum P H 61 6 14 77 Pseudomonas radiciperda p M 61 3 7 78 Liothrips setinodis I L 60 30 74 79 Diplodia zeicola P L 58 4 10 80 Cucurbitaria piceae P L 56 4 10 81 Eutetranychus orientalis I L 55 29 73 82 Agriotes obscurus I L 54 22 54 83 Sclerophtora raysiae P M 53 2 6 TABLE 4-1 (Cont. ) Rank Species Type Probability Of Establishment EEI Mid-Point EEI Range (Plus or Minus) Confidence Interval Direct Estimate 50% 90% 84 Amblyoma hebraeum I L 53 36 90 85 Chrysomyxa deformans P M 52 2 6 86 Chrysomyxa himalensis P M 52 2 6 87 Agriotes sputator I L 50 20 50 88 Nairobi sheep disease A L 48 16 89 Adelges japonicus I L 47 23 57 90 Adelges tardus I L 47 23 57 91 Spodoptera exempta I M 45 8 20 92 Thecopsora areolata P M 44 2 6 93 Ips typographus I L 43 57 136 94 Physopella zeae P L 43 7 17 95 Melanagromyza phaseoli I H 42 9 22 96 Monolepta discrepens I L 42 53 131 97 Macrosteles laevis I H 42 8 21 98 Panolis flammea I L 40 17 41 99 Heterodera rostochiensis P M 40 2 4 100 Pucciniastrum padi P M 39 2 5 1. Rank is based on the midpoint of Expected Economic Impact (EEI) 2. Type and number of species A = Animal diseases 16 P = Plant diseases and nematodes 49 I = Insects and mites 35 Total species 100 3. Probability of establishment is rated as High (25-99%), Medium (16-24%), and Low (1-15%). 4. Range is the distance from the mid-point to the maximum or minimum value. 5. The EEI range for the animal diseases was estimated directly rather than by use of the model. The data bank assembled by the Task Force can be used to assemble lists of pests that would attack specific animals or crops, and that could be carried by particular vectors. Examples of this are shown in the Report. Chapter 4 closes with a table showing how the 100 most dangerous species are distributed over the world. CHAPTER 5 - Programs for Foreign Protection The Task Force reviewed the approaches foreign governments have taken to protect their agriculture from exotic pests and diseases. While about 80 percent of them regulate one or more categories of arriving agricultural cargo, most of them do not try to intercept agricultural products brought in by arriving travelers. Only 20 percent regulate both incoming cargo and passengers. All of the regulatory techniques we employ are also in use somewhere else in the world. We didn't find any countries using promising techniques that were not used by us, with one possible exception. At least one country requires its returning animal husbandmen to have their shoes and clothes cleaned before returning to their farms. Although several hypotheses were advanced to explain the widespread policy of ignoring travelers as vectors of pest introduction, none stood up very well under examination, leading to the conclusion that there was tacit recognition in most countries that the ratio of risk reduction to cost for this particular pathway is small. Several of our attaches were asked to inquire about the existence of any assessments or evaluations of the agricultural quarantine programs that were being carried out in their assigned countries. None were found. The value and effectiveness of such programs is simply accepted on the basis of the presumptive evidence at hand. CHAPTER 6 - Programs for U.S. Protection The Task Force asked Vivian Wiser of ERS to prepare a history of agricultural import inspection work. The results of her research provide useful perspectives for the review of policies and programs. Chapter 6 begins with a condensation of that history which appears in full in the Appendix to the report. Following that there is a review of the program as it stands today, starting with a listing of the agencies involved in the inspection of personnel and cargo entering the U.S. The acknowledged objectives and strategy of the present program are considered and found to be too narrow in their definition, and an alternative is offered, to wit: The objective of plant and animal quarantine programs is to provide adequate protection to the plant and animal resources of the nation, while avoiding unnecessary restrictions on international trade and commerce. This will be done by encouraging shipments of clean cargo, fostering inspection at source, and by excluding or restricting goods, materials, or carriers as necessary to prevent the entry of those exotic plant and animal pests and diseases expected to cause great damage. The Task Force found that while the legal basis for the program provides sufficient authority to prevent the introduction of any exotic agricultural pest or disease, the quarantines and the quarantine manuals issued under the authority given us leave a lot to be desired. We recommend - and suggest a format for doing it - that the Quarantine Manual be completely rewritten so that it can easily be used by our employees in the field as an operating guidebook. Ideally, the Manual should contain a step-by-step outline of what inspectors should do from the time the carrier arrives until inspection of carrier and cargo has been completed in a manner which will result in reducing "pest risk" to a level acceptable to program managers. We also believe that the initiation, modification and termination of quarantines needs more systematic attention in view of the rapid change in trade and transportation technology. The issues of new transportation technology and new detection devices are considered at great length. Containerization will require a new configuration for the deployment of our personnel and different approaches to inspection. Bioluminescent sniffers are tools of great potential value in raising the effectiveness of our inspection efforts. Finally, the Task Force took a look at sampling and its application to quarantine inspections. The need to employ some kind of sampling arises from our manifest inability to look at everything. The argument is over the particular approach to take. The adoption of probability sampling will yield reliable information about the population of imported items we inspect. The institution of such a system will require considerable soul searching on the part of program managers, for they will have to decide what level of infestation they are willing to live with. Right now we are obviously tolerating some level of infestation. But because of our traditionally unsystematic approach to sampling, we don't know what that level is or how it may have been changing over time. In fact, our haphazard use of this powerful tool precludes an objective evaluation of our import inspection efforts. CHAPTER 7 - Assessment of U.S. Quarantine Efforts Recognizing that ignorance must account for much of the contraband plant and animal material brought to the U.S. by international travelers, the Task Force inquired of the APHIS Information Division as to their experiences with attempts to educate the traveling public. Although man-years expended in this effort have been small, the effort has resulted in: Inclusion of pertinent information in the passport and, after a long delay, on the Customs Declaration, and in the popular travel guides. Development of a working relationship with DOD on enforcement of AQI regulations with respect to returning personnel and retrograde cargo. Production and distribution of exhibits, publications, foreign language flyers, motion pictures and consumer interest features for newspapers, radio and T.V.; testing effectiveness of using direct messages with airline passengers; and use of direct message at Mexican border checkpoints. Information people have concluded that direct messages seem to be the best and most economical way of reaching travelers. They have also learned that airlines are positively not interested in helping AQI out with the direct message approach, and that cooperation between agencies in developing multiagency handouts for use by carriers, terminal operators, etc., is all but impossible to achieve. "Pestina, " the AQI identifying symbol, is miscast. Her sexy features are inconsistent with the "don't pick her up" message. The proportion of travelers receiving the APHIS messages is unknown, but for those who do and who wish to deliberately violate the regulations, there are two important incentives: It's o.k. if Customs doesn't find it and even if they do, the Customs or Agriculture inspector often allows it to pass; and the sanctions on discovery of contraband are trivial, if any. Not all products are, in fact, prohibited. The decision (made by a college graduate inspector) appears to be a service for travelers paid by the general public. Manifestly, maximum protection to that public would result from automatic confiscation by Customs, followed by immediate destruction. The major handicap in attempts to evaluate the agricultural quarantine program is the paucity of data that would throw some light on the effectiveness of AQI activities. The inadequacies of the cargo sampling procedures have already been noted. On another level, we are unable to associate new pest finds with something that happened at a port of entry. The data situation with respect to inspection of baggage for contraband is much better, even though they point to a conclusion which does not support baggage inspection as it is carried out today. Clearly, a major issue involved in enforcing agricultural quarantines is that of deterrence. Since a huge increase in manpower would be required to detect the low levels of infestation in cargo, and to intercept all the contraband, and since such increases are not in the cards, it follows that a major problem facing program managers is determining the number of policemen (inspectors) required to limit the number of attempts to bring in contraband or infested cargo to some tolerable level. Unfortunately, the learned journals and our law enforcement agencies have nothing to offer by way of theories of deterrence. The Task Force did, however, acquire a conception of the conditions necessary for deterrence to work. These, together with a discussion of penalties for violating AQI regulations, appear at the end of the section on deterrence in Chapter 7. Several examples of quarantines used as trade barriers are offered as evidence that quarantine programs are not without subterfuge. The Task Force Chairman interviewed a number of key airline personnel at Kennedy International Airport to assess program impacts on airline activities. In general, the airlines will actively oppose any rules or requests for cooperation which will raise their costs by so much as one iota. They do not wish to impair their competitive position in the field of transportation, and they are severely limited by government regulation as to the extent to which they can pass increased costs onto their customers. Major complaints were directed against AQI activities that increased dwell time for cargo, turnaround time for aircraft, and food waste. The Task Force invited all agricultural import inspectors to provide Dr. McGregor with their comments, complaints, and insights concerning the program. A disappointing number of responses was received (15), but their quality was high. Subjects drawing the greatest attention were: the sealing of ship's stores in galleys on freighters; lack of scientific information about pest establishment; need for a global approach to the problem; requirements for inspectors; preclearance and compliance agreements. Chapter 7 closes with a lengthy discussion of the problems involved in assessing the value of our quarantine efforts and a theoretical approach to maximizing the amount of protection with the available funds. Neither the data routinely collected as a part of program operations nor the program procedures as variously pursued at the many ports of entry fit into frameworks appropriate to cost-effectiveness analysis. The available evidence does not support any particular conclusion as to the value of the program. Thus, the effectiveness of our import inspection efforts remains a matter of speculation. CHAPTER 8 - Conclusions and Recommendations Major changes are needed in order to achieve the maximum reduction of risk that is possible with whatever resources are available. A transformed program should be based on these eight principles: Worldwide movement of pests should receive primary attention. APHIS should adopt a more balanced, realistic program goal. Effort should be concentrated on the highest risks. Biological uncertainties with respect to pest distribution, survival in transit, colonization characteristics, etc., should be reduced through the acquisition of new knowledge. Compliance, not enforcement, should be the operating philosophy. Private efforts to reduce risk should be encouraged. Explicit standards with respect to tolerable levels of infestation must be established. Both the framework and the data for evaluating the effectiveness of import inspection should be built into the program. In line with these principles, the Task Force recommends the development of a source inspection system which will provide incentives for exporters in foreign countries to ship us pest-free commodities, and sanctions if they do not. It involves shifting the cost of treatment and intensive inspection from general taxpayers to the exporters. The proposed Agricultural Source Inspection and Surveillance Technique (ASIST) involves mainly: Establishment of standards, source inspection of material, monitoring the performance of the exporters in the U.S. Recognizing that the development of ASIST will take a lot of time, the Task Force recommends several changes in the current program in line with the previously stated principles: 1. Revise strategies so as to concentrate on high risk species, with emphasis on exclusion as the appropriate policy. 2. Turn over passenger baggage inspection and the interception of contraband to Customs, eliminate the practice of allowing exceptions to be made as to the admissability of certain agricultural products, and monitor the performance of Customs in seizing contraband. 3. Eliminate border inspection of passenger vehicles. 4. Regulate germ plasm traffic more carefully. 5. Develop a Pan-American Quarantine. Whether or not ASIST is adopted, the following changes should be made in program operations: 1. Review and streamline regulations. 2. Establish uniform inspection procedures. 3. Employ statistical sampling. 4. Use new detection and control devices. 5. Test pathway survival. I INTRODUCTION 11 STATEMENT OF THE PROBLEM Responsible officials in the U.S. Department of Agriculture have long had an uneasy feeling about the efficacy of efforts to prevent the entry of exotic pests and diseases of plants and animals. The rapid increase in traffic at this time of budget restrictions limiting program effectiveness dictated the need for a close examination of current status, with the hope that some new procedures for dealing with risk from exotic pests might be found which would be more effective and less expensive. The problem is viewed as a matter that requires a complete examination of the U.S. policy of pest and disease exclusion and not as a matter of evaluating the efficiency of current programs. Alternatives for change in the present policy and programs will be severely circumscribed by constraints of budget, bureaucratic and organizational limitations, and attitudes in the political and industrial environments. There are many facets to the problem. Among the questions and considerations that led to this study are the following: II. I Disagreement on Objectives. There are different concepts of the purpose of the regulatory program. The program managers and indeed the inspectors themselves seem to believe that the objective is to protect U.S. agriculture by the complete exclusion of exotic pests and diseases. This is to be accomplished by permitting the entry of only those agricultural materials that have been inspected and found to be pest-free, or are so certified by other authorities, or by treating the materials to eliminate the pest or disease present. In addition, any imported material must be inspected to preclude the possibility that it is harboring agricultural pests. As a result, program accomplishment is reported in terms of the number of damaging pests that have been intercepted; i.e., excluded, from the U.S. On the other hand, a number of key policymakers, noting the rapid expansion in international trade and passenger traffic and the difficulty of obtaining resources for a program of exclusion, are more realistically considering development of a program based on risk reaction. The objective of such a program ought to be to limit the risk of importation to a level that can be tolerated by U.S. agriculture without a massive increase in personnel and funds. Thus, stress has developed between the policy officials and the program managers. The program people are frustrated and disheartened by the lack of resources which in their view are needed to carry out the program. Policy officials are frustrated because they can't get a real handle on program efficacy and are unable to visualize exactly the program configuration to be usefully employed. Furthermore, they find program people generally unwilling to experiment, committed as they are to a policy of exclusion. A policy analysis and an improved program design is needed. 11.2 Program Effectiveness. It is unfortunate that the numerical data on the regulatory program has to be treated empirically, because the figures cannot be analyzed statistically or scientifically. The number of inspections and the amount of contraband intercepted may be a measure of individual or unit work performance. However, the quantity of interceptions has no meaning as a measure of program effectiveness because its relationship to the total size of the import assault is unknown. Furthermore, there is no way of measuring the number of pests which have entered and failed to become established, or the number of challenges which are required to establish a pest. As a result, the Secretary's office and the Congress have no basis for determining the amount of resources that may be usefully employed. Managers have little guide to the deployment of their resources against flows of incoming materials. Nor is there any basis for responding to criticisms of program effectiveness. A significant number of pests and diseases have entered the country since 1884, when the program was instituted; e.g., Foot-and-Mouth Disease (3 times); Medfly (5 times); and Chestnut Blight. The recent findings at Kennedy Airport of a 50% probability of discovering agricultural contraband when present in passenger baggage certainly indicates that present procedures are not very effective in blocking that particular route of introduction. In addition, the findings raise fundamental questions: What should be the rate of contraband interception in order to achieve a significant reduction in risk? How much risk is associated with agricultural contraband in travelers' baggage? What proportion of the total risk of introduction is in airline passenger baggage vis-a-vis other pathways of entry? 11.3 Changes in International Traffic. The increased volume of passenger traffic entering the U.S. by air and by the land routes from Mexico and Canada places severe stress on the existing inspection force. The attempt to streamline inspection at Kennedy and other airports a few years ago was in reaction to the problem of rapidly increasing workload. Currently, the rising emphasis on stopping drug importations now takes first priority among the various reasons for inspecting passenger belongings. The rapid rise of containerization raises all sorts of questions about cargo inspection procedure and about the validity of any procedure. Since cargoes are often assembled in containers well within the boundaries of the exporting country, and since U.S. destinations are not only inland but widely diffused, traditional inspection sites at ports, whether of embarkation or entry, seem to be obsolete. Can containers be opened at a point of entry without undue interference with rapidly moving commerce and without reduction in the economic benefits inherent in containerization? If opened en route is inspection a practical matter, given the problems of access to the cargo? Consideration of the container itself as an environment in which the pest must travel requires detailed study. A substantial change is taking place in the relative importance of U.S. ports as an increasingly larger percentage of cargo enters the U.S. in containers. Inspection personnel ought to be deployed to meet this change. The expanding and shifting patterns of agricultural trade as developing nations begin to enter world markets and as the U.S. attempts to increase its own agricultural exports to benefit our balance of payments raise challenges to our present quarantine operation. All of these changes in international traffic will have effects on the risk of pest importation. Better understanding of these impacts and suggestions for adapting the program are needed. 11.4 Expanding Budgets. In the annual budget cycle it is necessary to consider the financial needs of the existing inspection and quarantine program. With the rising traffic volume there is a temptation to relate dollars directly to "workload," and to lose sight of the fact that what is being purchased is some amount of risk reduction rather than a number of inspections. What is the risk? How much risk reduction is being purchased by the present program operations? Doesn't more luggage and more cargo simply require more inspectors? If not in direct proportion, isn't there at least some relationship between traffic volume and resources required? No one appears to have satisfactory answers to these questions, and the annual decisions on budget are at the least uncomfortable, and at worst purely arbitrary. 11.5 Agency Relationships. Agency relationships, particularly with the Bureau of Customs, appear to be unsatisfactory. In passenger baggage, Customs receives funds from Agriculture to enable them to increase the volume of baggage that they would normally inspect. What volume does Customs consider "normal" to meet its responsibilities? How much additional inspection takes place? Does this increment meet Agriculture's needs? Are Agriculture's needs (standards) 100% inspection? Is the additional increment of Customs inspection purchased by Agriculture allocated to appropriate ports for high risk passengers in conformity with Agriculture's assessment of risk? How do inspectors decide whether imported foods are to be inspected by the Food and Drug Administration or by Agriculture? Is it improper to have these products inspected by both agencies? Does the Fish and Wildlife Service inspection for endangered species consider the likelihood of domestic animal diseases? How is it that the Customs job can be done with high school graduates, whereas Agriculture requires a college degree? Since Customs has the responsibility for enforcement of the Acts, is there a legitimate role for an agricultural inspector, where a Customs man is on duty? 11.6 Baggage Inspection Standards. Agricultural policy seems to emphasize 100% inspection of passenger baggage in order to secure adequate protection. Indeed, this is sometimes given as the rationale for the transfer of funds to Customs. Yet, the present rate of baggage inspection by Customs is estimated to be about 20% overall at our largest port of entry. Is the 100% standard possible? What standard is desirable? Is some standard less than 100% acceptable? 11.7 Improved Detection Capability. There has been remarkable technical achievement in sensors in recent years and many new devices are available or under development. What are the possibilities for such devices in baggage or cargo inspection? Should investments be made to adapt such technologies to the inspection process? These wide-ranging questions and considerations led to this study. It was hoped that answers might be found, or at least, that some new kinds of useful information could be provided. 12 OBJECTIVES The study has two objectives, agreed upon at the outset, as follows: -—To define and quantify the risks from the entry of those exotic plant and animal diseases that are major threats to our environment and our food and fiber supplies during the next twenty years. -—To develop and analyze strategies for protection against exotic diseases and pests. 13 APPROACH The approach puts together scientific, technical and administrative judgments from the best sources available. The study is partly descriptive, partly analytical, and partly judgmental. It includes background on the biology of major exotic pests and diseases, descriptions of trade patterns, developments in detection technology, economic assessment of probable losses, and comments on current performance. It is a compendium of many kinds of expertise and judgments. Domestic quarantines are excluded, as are domestic control and eradication efforts. Also excluded are the inspection and quarantine actions of the States, such as California and Florida. The relationships between Agricultural Quarantine Inspection and the major border inspection activities of the Department of the Treasury (Customs), Justice (Immigration and Naturalization), and HEW (Public Health) have not been explored. The study focuses on agricultural quarantine of exotic pests and diseases. Dr. Ned D. Bayley, Director of Science and Education, when the study was initiated, posed the objectives, sought to formulate the major questions, and encouraged the Task Force. The study was undertaken at the request of Dr. Francis J. Mulhern who provided for the participation of the Task Force members, and periodically reviewed progress. The original design for the study was formulated by Mr. Richard D. Butler, Director of the Planning and Evaluation Staff, APHIS. In addition, Mr. Butler monitored the day-to-day operations of the study, working closely with the Task Force Chairman. The study was conducted under the leadership of Dr. Russell C. McGregor of the University of California, who was employed by the Animal and Plant Health Inspection Service (APHIS) as a part-time consultant. Dr. McGregor was responsible for conceptualizing the problem, selecting the Task Force members, establishing the study procedures, assigning tasks, and writing the final report. While the members of the Task Force are in overall agreement on the content of the report, they do not necessarily support each of the final conclusions and recommendations. These are the responsibility of Dr. McGregor. It was agreed that the study might propose new laws, policies and the most effective programs to reduce risk, including trials of new procedures and methods, or more effective configuration and deployment of existing quarantine efforts to increase the probability of exclusion. The proposals were to be operationally feasible and reviewed and critiqued by APHIS program managers prior to submission of the report; they did not need to be limited to actions that could be taken within existing funds, nor need they be limited by existing laws or policies. Detailed organizational plans were not required, since they could be developed by APHIS officials subsequent to completion of the study. 14 PROCEDURE Having agreed upon the objectives and the general approach to the problem, the procedure for carrying out the study consisted of five operations. First, an outline was prepared of the principal analytical issues and critical questions to be considered by the study. This outline included a discussion of seven topics. Their titles were as follows: --Major International Pest and Disease Threats --The Consequences of Introducing Exotic Pests --International Pathways of Pest and Disease Movement --The Effectiveness of Quarantine Programs --Protection as a Concept --Increasing the Future Supply of Protection --New Programs These topics served as a working outline for the final report. They also provided the framework to identify the individual tasks that needed to be done. Second, 36 separate tasks were described, assignments of personnel were made, and deadlines established.1 Each description included the title, objectives, assignment, performer, time, deadline, product, and approach. Third, a critical path flowchart was laid out illustrating the span of working time for each task and its relationship to other tasks.2 This chart, termed a "Game Plan," also arranged the tasks according to the kinds of talents required; i.e., entomology and pathology; psychology and sociology; history, law, policy analysis; economics; engineering and transportation; statistical analysis; organization and management; synthesis and interpretation. In addition, the Game Plan called for 12 output and recommendation papers to be produced during the year-long study. As expected, there were many alterations made along the way, and the deadlines required constant readjustment. Fourth, six Task Force members, knowledgeable in some aspect of the problem, were selected to assist in getting the task completed. At the first meetings the objectives, the outline of issues, the task outlines, and the Game Plan prepared by the chairman were reviewed and revised. At subsequent meetings progress was reviewed, status reports were prepared, and plans were updated and revised. Finally, the chairman prepared a draft from the papers submitted for each of the tasks. Each member of the Task Force reviewed and critiqued the draft, resulting in this final report. 1. A complete list of titles of the tasks is in Appendix 1-A. 2. A copy of the Game Plan is Appendix 1-B. 2 THE ARRIVAL OF IMMIGRANT SPECIES 21 THE POTENTIAL FOR INTRODUCTION The continental United States has been and is particularly prone to pest introduction. It is a large land mass settled and developed agriculturally in 500 years. Our crops are introductions for the most part. Pests were in many cases introduced with these crops. The "melting pot" of ethnic groups, it is likewise the melting pot of crops and pests. In 1919, J.A. Stevenson of the Bureau of Entomology and Plant Quarantine listed 120 foreign plant diseases known to have been introduced into this country, and commented that the list was far from complete both because all present are not recorded and because those introduced in earliest colonial times were not so recorded. Some rusts and smuts of cereals are in this category. The appearance of additional foreign pests has continued since that accounting and there is no doubt that introduction and establishment continues. For example, the Dutch Elm Disease was first noted in Ohio in 1931, the golden nematode of potato in Long Island in 1941, witchweed of corn in 1950 - these are only a few. A recent listing by A.J. Watson, 1971, lists 1,492 bacterial and fungal diseases foreign to the United States, and the listing excludes viruses, nematodes and all diseases of forest trees. No one can say with certainty how many different kinds of insects are included in the total world fauna. We know that somewhat more than 900,000 have been named. Conservative estimates of the actual number of species range from 2.5 to 5 million. Of those named, detailed knowledge of the behavior, biology, and ecological requirements of all life stages is available for no more than 10,000. Among the vast array of insects and related anthropods there exist species adapted to fill almost any conceivable ecological niche. It is doubtful that any terrestrial or fresh water plant or any land animal is immune from some form of insect attack. While many insect-host associations are mutually beneficial and others benign to the host, many insects and mites are able to completely destroy their primary host. This may be due to direct utilization of the host as food or indirectly as the vector of disease. The fact that plants and animals are able to coexist in communities and ecosystems is a consequence of evolutionary processes that interpose checks on the disproportionate increase of any member of the ecological community - be it plant, animal, insect or pathogen. These checks take the form of host resistance and natural enemies adapted to utilize other organisms as food. The mortality caused by an attacking insect commonly elicits some form of defensive response that tends to protect the host. At the same time natural enemies respond to increased numbers of a host by causing progressively greater mortality, and thus become regulative. This chapter is based on material contributed by the Task Force Scientists: Reece Sailer, Charles Kingsolver, and Don Johnson. Since ecosystems evolved long before man became an important force in evolution, their stability was determined by factors of climate, geography and isolation. During the past 5,000 years man has modified the environment at an accelerating rate. Through his agriculture and other impacts on environment he has created new, usually much less complex, ecosystems that became increasingly vulnerable to disruption through pest attack as the area and intensity of agriculture grew. Initially these effects were small and confined to areas where crop plants and livestock were first domesticated. However, the age of discovery that began when Columbus discovered America in 1492, set in motion changes that affected the world biota on every continent and most islands. No continental area has been more affected than that of the United States. During the past 480 years the geographic barriers provided by the Atlantic and Pacific Oceans have been breeched by man's commerce, and the ecology of the continent changed by his agriculture and other activities. In developing the agro-ecosystems that now occupy most of the United States, European immigrants adopted and greatly expanded the culture of such native crop plants as corn, cotton, potatoes, and tobacco. They brought with them wheat and other small grains, forage crops, livestock, vegetables, and fruit trees. Inadvertently they also brought weeds, insect pests, and pathogens. Many thrived because they were unaccompanied by natural enemies that were present in the agro-ecosystems of Europe. Others failed to overcome the natural ecological barriers to colonization. As commerce to other parts of the world increased new pests and diseases continued to arrive. 22 THE PATHWAYS 22.1 Historical Pathways. Insects and pathogens foreign to North America have been gaining entry and colonizing favorable habitats within the boundaries of the United States for at least 350 years. The successful immigrants for the most part have been those best adapted to survive in the pathways of entry and fortunate enough to find a favorable environment in which to live and reproduce once they arrived. Initially the successful species were those associated with man (bedbugs, body lice), his stored products (granary weevil, angoumois grain moth, cheese mites, etc. ), and his livestock (house fly, cattle grub, and horse bots). These were species that could survive a long sea voyage because they remained associated with their food supply. During this early period of colonization the entry of animal pathogens with importations of livestock was probably constrained by the long sea voyage. Animals weakened by disease could not survive and were disposed of at sea. During this early period and continuing until comparatively recent times, ship ballast provided means for the entry of many soil-inhabiting pests. Those that arrived early by this route were mostly innocuous or even beneficial forms such as ground beetles, but later arrivals included such notorious pests as the imported fire ant, and white fringed beetle. As settlement progressed and permanent agricultural communities became established, nursery stock for planting of orchards was imported, accompanied by a variety of such pests as fungal, bacterial and viral pathogens, scale insects, aphids, and codling moth. With arrival of additional human immigrants from different countries new kinds of crop plants and additional kinds of insects and plant pathogens were added to American agro-ecosystems. The new species often found previously pest-free crops and an environment where natural enemies were largely absent. The resulting population explosions of pest species were an all too common phenomenon and in good part explains why the United States very early gained world leadership in the field of plant pathology and economic entomology. Until comparatively recent times, as might be expected, most of the invading species came from Europe. However, from the last quarter of the 19th century through about 1915, as the source of imports shifted, there was a large influx of immigrant species from many other parts of the world. Many of these were insects belonging to groups that feed by sucking the sap of their host plants. They were the scale insects, aphids, thrips, and mites. More than 200 such species arrived with serious and often catastrophic effect to citrus and deciduous fruit production, as well as to a great variety of ornamental plants. Unquestionably living plants, the soil in which they were rooted and their seeds or fruits, have been a pathway of entry for a majority of the foreign fungal and insect species and the nematodes and viruses now in the United States. It was not until the middle of the 19th century that farmers and agriculturalists became acutely aware of the economic significance of the losses to our agriculture caused by pests and pathogens being introduced with imports from foreign countries. The epizootics of contagious bovine pleuropneumonia (1843) and Foot-and-Mouth Disease (1870) led to the appointment of specialists to study the diseases. Reports of these studies included evidence identifying countries of origin, importers, pathways of entry and the economic impact of the disease. Unquestionably, there were prior incursions of pests and pathogens of crops and livestock of equal or greater economic significance; however, the disease was either less dramatic in appearance at the time of entry, or the origin and economic impact was obscure. These studies increased our awareness of the vulnerability of our developing agricultural industry to foreign pests and diseases and gave impetus to the enactment of legislation authorizing the quarantine of imports to reduce the threat. For 1972, the Bureau of Customs reports that the pathways of entry consist of an estimated 70 million carriers of persons and merchandise arriving in the U.S. from foreign countries. More than one-half of those were vehicles entering from across the Mexican border. This volume of traffic is steadily increasing. 22.2 Aircraft. Since 1940, aircraft have assumed increasing importance as a pathway of entry. The rapidity with which planes move from one part of the world to another allows short-lived, winged adult insects and infective propogates of plant pathogens to survive transit and escape into new geographic areas. The number of planes involved, and the number of distant locations that may be visited on a single flight, increases the magnitude of this threat. Many of the new exotic additions to our North American insect fauna will arrive by aircraft. Among these insects are those which serve as vectors of plant virus diseases. It is possible that viruliferous insects could survive this pathway to introduce new virus diseases. Short-lived spores of plant pathogens will also enter by this route. 22.3 Scientists as Pathways. The airplane has accentuated another problem that has long existed. For a variety of reasons biologists frequently wish to use exotic pests and plants as objects of experimentation. Often this is because a foreign scientist has used these species in his research and has developed background knowledge of a kind essential as a starting point for the American scientists' research. In other instances a traveling scientist is tempted to bring breeding stock to his home laboratory because it has characteristics that pique his curiosity. Once such an organism has become the subject of some unusual research contribution, other scientists will often wish to obtain cultures. Unquestionably, certain exotic species of cockroaches have become naturalized as a result of this kind of dispersal. We may expect that this avenue of entry will become more important as a result of increased interest in research on genetic control of a variety of pests and diseases. In this case, the danger is often that of increasing the gene pool of an already established pest, but there is also the danger of introducing closely related species having different potential as pests. This could be the result of deliberate introduction for use as sterile hybrids in control experiments or inadvertent introduction of species thought to be the same as an established pest. Where such research is conducted by competent, responsible scientists under adequate quarantine, no significant hazard will be involved. However, competency, responsibility, and adequacy are all relative terms and any such research should be kept under strict surveillance by competent regulatory personnel. A more serious danger is the scientist who wishes to bring in an organism but is either unaware of regulations or deliberately chooses to ignore such regulations. He may correctly regard his plant or insect to be entirely harmless, but what he may not recognize or have the competence to detect are associated pathogens and potentially injurious parasites. When such efforts to introduce organisms in violation of regulations are detected they should be investigated. Undetected violations are sometimes discovered later, as the scientist is likely to publish results of research involving the illegally imported organisms. If the violation has resulted in any adverse economic effect, or could have done so, the violator should be held responsible and the matter fully publicized. 23 COLONIZATION AND ESTABLISHMENT 23.1 Food Resources and Environmental Resistance. One of the principal characteristics of all living organisms is their innate tendency to exploit food resources to limits imposed by their environment. Where the entire resource is within bounds of limiting environmental factors both the organism and the resource are in jeopardy of extinction. In long established ecosystems evolutionary processes establish mechanisms that allow the organism and a self-replenishable resource to coexist. In the case of insects and the plants on which they feed, the accommodating mechanisms take a variety of forms. One of the more common is some form of host resistance whereby the plant imposes limitations on the fecundity or survival of the developmental stages of the insect. A second mechanism is one that pervades all ecosystems; this relates to the role of natural enemies whereby a plant-feeding insect is in turn the food resource of one or more other organisms. Like host resistance, the action of the natural enemies imposes limits on the ability of the plant-feeding insect fully to exploit its host. These fundamental characteristics of host-exploiter relationships and ecosystem evolution are critical to an understanding of the objectives and operation of agricultural quarantine and pest control programs. One of the explanations for the successful invasion of new organisms lies in the post-Pleistocene history of the North American flora and fauna. Following the withdrawal of the last continental ice sheet about 10,000 years ago, the North American biota reoccupied the glaciated areas and species assorted themselves into life zones and biomes according to their environmental requirements and to limitations imposed by internal ecological or geographic barriers. Except as they made use of fire, the aboriginal inhabitants had little influence over the history of the ecosystems that evolved in North America prior to the arrival of Europeans. However, within a few years after Columbus made landfall at the island of San Salvador in 1492, events were set in motion that were to affect the North American biota more profoundly than did the glaciers of the earlier epoch. With the arrival of the Spaniards, Frenchmen, and Englishmen, came the livestock, field crops, horticultural crops and ornamental plants of Europe, accompanied by camp-following insects, weeds, and diseases. As the population of the U.S. increased, the number and size of the farms increased to meet the demand for food. The increased acreage of crops and herds of livestock enhanced the probability that a susceptible host would be exposed to and infected by a foreign pest or pathogen that might enter. The concentration of the industry increased the potential for diseases to spread and become established. As agriculture spread across North America, commerce reached out to all parts of the world, and additional alien species gained entry and became part of the North American biota. 23.2 "The Sweepstakes." It is evident that there is an unknown, but very large number of foreign insects, bacteria, fungi, viruses, and nematodes that are potentially dangerous to the agriculture and environment of the United States. These may number 6,000 insects alone. On the basis of past experience we can predict that a certain number of these species may gain entry in a given period of time, but we cannot predict their identity. We can predict with greater reliability that certain notorious pests such as the Mediterranean fruit fly and the Khapra beetle will be excluded during the same period, but even here the confidence limits are not reassuring. These potentially dangerous species are ticketholders in a sweepstakes lottery. A relatively small number of the species hold a disproportionate number of the tickets and thus increase their chance of entry. Many of the tickets are lost in the pathways of entry. Since the sweepstakes are illegal in the U.S., any tickets found by quarantine inspectors are confiscated and destroyed. Before the final drawing inside the United States the ticketholders are subjected to a series of chance hazards and a final fitness test. With few exceptions, each of the 6,000 or so pests on our list will almost surely not become established in the U.S. in the next few years. Yet, it is almost surely true that some of them will become established here. This paradox points to the futility of gearing countermeasures to a pest-by-pest approach. We cannot have a thousand programs to counter a thousand unlikely pests. Some will get through. Once past the quarantine barrier, the pests, represented in the case of insects by perhaps no more than a single fertilized female, must find a food source. If such a female is adapted to the subtropical climate of Florida, and finds herself on the ground at Kennedy airport, she is a loser. On the other hand, if the same female manages to make it over the fence of the Miami, Florida, airport, chances of finding a favorable habitat for her progeny are vastly improved. However, a chance encounter with a hungry ant, bird, or other predator, may eliminate a potential winner. But assuming that the gravid female survives all hazards and produces her allotted number of progeny, these must survive and reproduce. Numerous hazards continue to confront the incipient population. Weather, the availability of food, and predators threaten extinction. But, perhaps of greater importance, behavioral and genetic characteristics now may determine the success or failure of permanent establishment. If the species is parthenogenetic, then it has a great advantage. In a bisexual species, the individuals of different sex may mature at different times, and may exhibit a dispersal phase between adulthood and sexual maturity, that is genetically determined. This can easily result in the failure of the females to find mates when they are sexually receptive, and a consequent failure to colonize. As in the insect case cited, plant pathogens face a somewhat similar sequence of probabilities. The infective propagule must be transported except for those with airborne spores - to a susceptible host crop and arrival must coincide with environmental conditions required for infection. Probability of success is extremely low, but propagule populations are high and resistance of some fungal spores and of nematodes to adverse environmental conditions is astounding. 23. 3 Genetic Barriers. Assuming that the first generation of females have found mates and food resources are abundant, there remains a genetic barrier to successful establishment. This is the genetic load of recessive, deleterious and often lethal alleles that are present, to some degree, in all organisms. This genetic load differs between species, and within a species may vary between populations. To avoid the deleterious effects of the genetic load, most bisexual organisms have evolved mechanisms to prevent inbreeding. In the case of man, laws against incest serve this purpose. Where close inbreeding occurs, as it does in a new immigrant population, any recessive deleterious alleles have a high probability of becoming homozygous, and the recessive characteristics they determine will be expressed. This commonly results in reduced fecundity, high mortality during development, and the shortened longevity of adults. It is the frequent cause of loss of laboratory cultures of insect species maintained through several generations. If, despite this reduction in reproductive potential, an incipient immigrant population can survive through several generations, it may eventually reduce its genetic load sufficiently to restore genetic vigor. This would result from selective elimination of deleterious alleles from the gene pool. There is also the chance that new arrivals would permit restoration of genetic vigor through outbreeding. Obviously, this final obstacle to establishment of an immigrant population will be affected by the number of colonizing individuals as well as the level of genetic load of the population and mating behavior characteristics of the species. In view of the hazards encountered in the pathways of entry and obstacles to be overcome during early stages of colonization, the number of "sweepstake winners" is remarkably high. This again points to the overriding importance of an adequate food resource and the absence of appreciable environmental resistance as dominant factors in the success of invading species. Quarantine measures may change the odds, but they cannot change the basic rules of the game. 24 THE RECORD OF ESTABLISHMENTS Under the leadership of Dr. Reece I. Sailer of the Task Force, a survey of adventive insects known to be established in the continental United States was undertaken, with the help of the taxonomists in the ARS Systematic Entomology Laboratory and the Smithsonian Department of Entomology. While not complete, the resulting list now includes 1,115 species. The insects and mites that comprise this list gained entrance during the past 480 years and have become part of the North American fauna. None were deliberately introduced by man, yet few, if any, would have reached the United States through natural pathways of dispersal. Fewer still could have founded colonies without the substantial changes in food resources and the reductions in environmental resistance caused by the development of agro-ecosystems. While 1,115 species may appear to be an impressive number, it is in fact only about one percent of the total insect and mite fauna of the continental United States. Yet this one percent includes pest species that account for a great part of the losses caused by pests. In assembling the list of adventive immigrant species, a date of earliest known occurrence in the U.S. was established for as many of the 1,115 species as possible. Such dates were fixed for 955. Admittedly, such dates for many of the species are the accident of collection or of study by a taxonomist, and the rate at which they are discovered may reflect the amount of effort expended in searching, as much as any other factor. In most cases, a species would have been in the United States many years before it was collected and identified, and it would be hopeless to attempt to pinpoint the year of arrival. This is particularly true in the earliest years, when there was a scarcity of talent for identification. Nonetheless, it is of interest to examine the historical record of new alien species as recorded by their earliest known occurrence in the United States. Table 2-1 is a listing of immigrant insect and mite species, not purposely introduced, according to their estimated time of arrival in the United States. The record includes only the 48 contiguous States. Introductions in the 17th and 18th centuries are mostly those inferred by the known habits of the species, although reasonably accurate dates can be fixed for a few. For example, it is known with some certainty that the Hessian fly became established in 1778, and the boll weevil in 1892. These insects caused so much damage that the time of their introduction was widely noted. In view of the nature of the records, however, it seems appropriate to lump the early data into 100-year periods. Following 1800 the records are treated as totals for 20-year periods, and after 1900 the quantity and quality of data is such that 10-year periods are used. Note that dates of arrival have not been established for 160 species. Table 2-1 also lists the average number of new species established per year, in each of the periods of record. This reveals a rapid increase up to about 15 species per year in the 1910-1919 decade. Since about 1920, the rate of establishment of new species has stabilized at between 8-1/2 and 9 species per year. This information is presented graphically in Figure 2-1. TABLE 2-1 NUMBER OF IMMIGRANT SPECIES OF INSECTS AND MITES, * BY PERIOD OF FIRST KNOWN ESTABLISHMENT IN U.S. ** Period of Establishment Number of New Species Established Average Number of New Species Established Per Year Cumulative Number of New Species Established 100-Year Periods: 1600 - 1699 13 0.1 13 1700 - 1799 17 0.2 30 20-Year Periods: 1800 - 1819 9 0.4 39 1820 - 1839 22 1.1 61 1840 - 1859 13 0.6 74 1860 - 1879 53 2.6 127 1880 - 1899 105 5.2 232 10-Year Periods: 1900 - 1909 115 11.5 347 1910 - 1919 153 15.3 500 1920 - 1929 86 8.6 586 1930 - 1939 92 9.2 678 1940 - 1949 80 8.0 758 1950 - 1959 96 9.6 854 1960 - 1969 83 8.3 937 Recent Period: 1970 - 1972 18 6.0 955 Unknown Period: 160 - - TOTAL 1,115 * Excludes those species that were purposely introduced. ** Includes only the 48 contiguous Suites. FIGURE 2-1 NUMBER OF IMMIGRANT SPECIES OF INSECTS AND MITES ESTABLISHED IN THE U.S. The fourth column of Table 2-1 lists the cumulative number of new species established, excluding the 160 for which datas have not been established. This data is also displayed graphically in Figure 2-1. It will be noted that the number of alien species increased very slowly prior to 1860. Following this date, the curve of the line rises steeply, until 1920, when there is a modest deflection of the slope, which then continues as a nearly straight line to the present date. The deflection of the nearly exponential curve to a straight line following 1920 is a puzzling phenomenon. In addition to the increasing volume of trade following 1920, the later time period includes the advent of air travel. There was a burgeoning increase in ship and aircraft arrivals and a remarkable decrease in transit time between foreign and U.S. seaports and airports. These factors should have increased the rate of introduction of foreign species and the establishment of colonies. At the same time, there was an increasing number of entomologists engaged in research, regulatory and control activities. This factor would presumably decrease the time lag between establishment and discovery. Quarantine exclusion measures may also play a role.1 However, to whatever extent quarantine measures are able to focus of?? pest organisms, rather than on all immigrant species, their influence on the rate of introductions will be selective, rather than providing a general restraint. Increasing environmental resistance due to the rapid filling of ecological niches in the prior period may also be a part of the explanation. Unfortunately, the data do not appear to provide a basis for deciding on the relative importance of these influences, and the decreased rate of establishment since 1920 remains unexplained. 25 THE HAWAIIAN EXPERIENCE The Hawaiian Islands are remarkably well suited to the study of factors relating to invasion of foreign organisms. The climatically favored islands have never been connected to any continental land mass and have been geographically isolated from the world biota since their origin several million years ago. Prior to the arrival of Europeans in the 18th century, the islands were populated by a fauna and flora derived from waif species that have been estimated by Zimmerman to have arrived at a rate of one per 50,000 years. During the past 250 years, the native fauna and flora have been in good part displaced, and many species reduced to extinction as a result of invasion by nonindigenous man, his crop plants, domestic animals, and camp following weeds and other organisms. It was early recognized that the crops which thrived when first introduced were highly vulnerable to insect pests that either accompanied the imported plants or gained accidental entry at a later date. This problem was so serious that Hawaii early recognized the importance of importing parasites and predators and was remarkably successful in obtaining biological control of most of the pests. 1. The effectiveness of quarantine exclusion measures is discussed in Section 73. At the same time, Hawaii became aware of the importance of excluding foreign pests and for many years has maintained a quarantine inspection program more rigorous than that of the continental U.S. This effort was facilitated by the fact that most imports came through a single port, Honolulu. Although an active center of commerce, as a way station across the Pacific, the total volume of commerce has been only a fraction of that of continental U.S. With these factors in mind, a list of insects immigrant to the Hawaiian Islands has been compiled. In developing the list, information provided by the Hawaiian Department of Agriculture was most helpful, but again, much information was obtained from the taxonomists of the ARS Systematic Entomology Laboratory and those of the Smithsonian Department of Entomology. Interestingly enough, this list includes almost the same number of species as are included in the list of species immigrant into continental U.S. While again not complete, 1,041 species of insects and mites have been recorded as immigrant to Hawaii, compared to 1,115 for continental U.S., as shown in Table 2-2. TABLE 2-2 COMPARISON BETWEEN THE UNITED STATES AND HAWAII IN THE NUMBERS OF IMMIGRANT SPECIES OF INSECTS AND MITES Continental U.S. (48 Contiguous States) Hawaii Number of Ports of Entry 30+ 1 Number of Immigrants (species) 1,115 1,041 Number of Dated Immigrants (species) 955 955 Number of Immigrants, 1942-72 (species) 250 244 Percent of Dated Immigrants, Arriving in 1942-72 26 26 Area (thousands of square miles) 2,977 6 Rate of Colonization, 1942-72 (species per thousand square miles) .08 40 It is a remarkable coincidence that of the 955 immigrant species in Hawaii for which earliest dates of known occurrence are available, 244 are recorded for the period 1942-72. This is 26% of the dated species and precisely the same percentage figure as that for the 1942-72 period for the 48 contiguous States. In attempting to place these figures in perspective and interpret their significance, several aspects of the problem must be examined. The land area of the Hawaiian Islands is only 0.2% that of continental United States. Where Hawaii has one port of entry, the mainland States have more than 30, and in addition, the latter has several inland international airports that provide potential pathways into the heartland of the country. Hawaii, in proportion to its land area, has a very much larger number of entomologists, and in terms of volume of commerce, a larger quarantine inspection force. Although there is a much greater diversity of crops and habitats within the continental States, these are dispersed over a vastly larger land area. In Hawaii, where the overall diversity is less, the various habitats are more readily accessible from the principal port of entry. The more moderate and stable climate is also more favorable for an invading species than is the climate over much of the continental States. A well established principle of zoogeography states that when two species from different geographic areas come together and compete for the same ecological niche, the species from the larger land mass will displace the species native to the smaller land mass. This results in a remarkably high rate of colonization in Hawaii. As shown in Table 2-2, in the period 1942-72 the rate of colonization per thousand square miles was 40 species, 500 times the rate of the continental U.S. With these facts in mind, what conclusions can be drawn from a comparison of the immigrant insect faunas of Hawaii and the 48 contiguous States? First of all, it would appear that it is very much easier for an insect to gain entry and establish a population in Hawaii than in continental U.S. Or, put another way, the obstacles to invasion of the continental States are much greater than are those in Hawaii. Are these obstacles those imposed by quarantine inspection activities? This seems unlikely, for Hawaii has a more strict and rigorously enforced quarantine program than do the 48 continental States. Geographic isolation cannot be the important barrier since the 48 States are contiguous with Mexico and Canada. The volume of commerce is certainly not involved since that to Hawaii is only a fraction of that entering the ports of the contiguous States. We are left with the only possible conclusion - there is a very much higher probability that an insect will establish a colony once on the ground in Hawaii. This, in turn, implies that it is not the deterrent effect of quarantine inspection but rather some ecological difference between Hawaii and the contiguous States that accounts for the disproportionately low immigrant fauna present in the latter area. Pronounced ecological differences are readily apparent in the biotic characteristics of insular and continental faunas. One of the most marked differences in degree of diversity resulting in insular ecosystems being less complex and accordingly less stable than the more complex ecosystems characteristic of continental areas. We may, therefore, conclude that North American ecosystems are more resistant to invasion than those of Hawaii. While true of both agro- and natural ecosystems, it is evident from the list of immigrant species that most of those now resident in North America are associated with man-modified environments. Where, as in natural forests, the native biota have remained little affected by man, there are few immigrant species. In Hawaii, on the other hand, the native fauna and flora seen unable to resist invasion and displacement by foreign species. 26 IMMIGRANT SPECIES AS PESTS With the settlement of North America by Europeans, vast food resources became available that were vulnerable to exploitation by Old World insects. When these insects gain entry to North America they are normally not accompanied by the natural enemies that tend to regulate their abundance. Native natural enemies being poorly adapted to exploit the new arrivals, and the crop plants having developed in areas where natural enemies were the dominant limiting factor, the newly arrived insects increase with little or no restraint. The result may be catastrophic destruction of the host plants. These often catastrophic out-breaks of a recently arrived pest present a problem all too familiar to farmers, orchardists, and foresters. These people, as well as many entomologists employed to find methods for control of such pests, are often at a loss to explain why such alien species should be serious pests in the United States when they often have little or no importance in their home country. For the most part, these immigrant species are associated with man-modified environments which encompass all agro-ecosystems. Within these ecosystems the immigrants tend to be much more disruptive than they are in the homeland systems from which they came. The reasons for this difference must be sought in the evolutionary history of agro-ecosystems. In the Old World these systems evolved over a period of several thousand years, during which man domesticated and improved indigenous crop plants. Associated with these crop plants were numerous indigenous pests that accompanied the plants into the new agro-ecosystems. The pests were in turn accompanied by natural enemies specialized to exploit individual pest species as a food resource. These enemies functioned as agents that regulated the abundance of the pest species and tended to prevent explosive outbreaks of the kind so often experienced when the same pests invaded North America. Several factors are responsible for the failure of natural enemies to accompany their hosts to the United States. First of all, an enemy species is normally less numerous than its host, and thus is less likely to enter an entry pathway. Once in the pathway it is more likely to be eliminated, again because of the effect of smaller numbers. But, of even greater significance is their status as secondary consumers. As part of an ecosystem, crop pests are primary consumers and so compete directly with man for the same food resources. A pest of a crop plant arriving in the United States finds an abundant food supply, but the natural enemy, as a secondary consumer adapted to utilize the pest as a food resource, is in double jeopardy. It must not only survive transit but also find a population of its host. Clearly, the entry pathway and process of colonization acts as a selective filter through which pests can pass more readily than parasites, predators, and pathogens. Plant quarantine measures tend to make the filter more impervious to entry of both pests and their natural enemies, while beneficial insect introduction programs are designed to facilitate entry of the secondary consumers needed to stabilize agro-ecosystems. Thus, American agro-ecosystems are not only already subjected to the adverse effects of a past imbalance between immigrant pests and their natural enemies, but they remain highly vulnerable to a vast assemblage of alien pests than have as yet failed to gain entry. Yet not all of the 1,115 immigrant species of insects and mites become pests. Some species even prove beneficial. Figure 2-2 is a classification of species that have immigrated to the 48 contiguous States. In Table 2-3, 50 percent of the immigrants are shown to be pests, and only 212 of these, or about 19 percent of the immigrants, are considered important pests.1 These include, however, many of the more serious pests of American agriculture and account for about 50% of the total pest losses in plant agriculture and horticulture. This estimate excludes forests, which have not suffered so severely from foreign insect invaders. Of the 616 immigrant pest species, 6 have been eradicated since their introduction, and 10 are believed to be naturally extinct. Two of the minor pest introductions were deliberate, rather than accidental. One-fourth of the immigrants have proven beneficial. That is, they are known to be enemies of pest species or belong to insect groups known to be mostly or entirely predacious. As such, these 278 species are plus factors in maintaining the stability of the ecosystems in which they live. Somewhat more than 600 attempts have been made to introduce beneficial species, but only about 420 of these efforts reached the field level. As a result, 126 beneficial species have been deliberately introduced. Two hundred twenty-one species, about one-fifth of all the immigrants, have proven to be of no particular importance. 1. For comparison, in Hawaii 75 out of the 400 immigrant insect species, or 19 percent of those arriving in the 25-year period 1937-61, were found to be of "some economic or medical importance. " See Beardsley, John W. 1962, On Accidental Immigration and Establishment of Terrestrial Arthropods in Hawaii During Recent Years. Proceedings of the Hawaiian Entomological Society for 1962 XVIII (1) 102 Aug. 1962. FIGURE 2-2 TOTAL NUMBER OF IMMIGRANT INSECT SPECIES TO THE 48 STATES: 1, 115 1/ Includes 2 introduced deliberately. 35 of the 404 minor pests are important in their countries of origin. 2/ Prior to introduction. TABLE 2-3 ECONOMIC IMPORTANCE OF IMMIGRANT SPECIES OF INSECTS AND MITES ESTABLISHED IN THE U.S. * Relative Economic Importance Accidentally Introduced Deliberately Introduced Total Immigrant Species Percent of Immigrant Species Important Pests 212 212** 19% Minor Pests 402 -- 404** 36% Beneficial Insects 152 2 126 -- 278 25% No Importance 221 221 20% TOTAL IMMIGRANT SPECIES 987 128 1,115 100% * Includes only the 48 contiguous States. ** Six of the pest species have been eradicated and 10 are believed to be naturally extinct. 26. 1 Predictability. A comparison of the behavior of these immigrant species in their original overseas habitats with their impacts in the U.S. reveals significant differences. As shown in Table 2-4, of the 212 immigrant species which became important pests in the U.S. only 73 were expected to be important, based on present knowledge of their economic significance in the country of origin. Thus, the behavior of two-thirds of the important pest immigrants came as a surprise to entomologists. So did most of the minor pest species; only 35 species were expected to be of minor pest importance and there were 367 "surprises" that proved to be such. Overall, only 18 percent of the immigrant species that proved to be either important or minor pests in the U.S. would have been expected to behave as they did. TABLE 2-4 EXPECTATIONS CONCERNING THE BEHAVIOR OF IMMIGRANT PEST SPECIES Relative Economic Importance Pest Behavior Total Pest Species Expected Not Expected Important Pests 73 139 212 Minor Pests 35 367 402* TOTAL PEST SPECIES 108 506 614 PERCENT 18% 82% 100% * Excludes 2 minor pests that were deliberately introduced. There has been, therefore, a high degree of unpredictability about the likelihood of exotic insects becoming pests. Presumably, this uncertainty is susceptible to reduction by an expansion of scientific knowledge about species resident overseas, and an investigation, or simulation, of the possible availability of U.S. ecological niches prior to the arrival of the species. 26.2 Relative Importance. Within the geographic boundaries of the 43 contiguous States there are about 10,000 kinds of insects, mites, and ticks having some degree of importance as pests. Of the approximately 700 that fall in the category of important pests, only 212, or 30 percent of the total, are of foreign origin. These include many of our most serious pests, as exemplified by the European corn borer, gypsy moth, boll weevil, Oriental fruit moth, European pine shoot moth, and the alfalfa weevil. In spite of the great importance of immigrant species as pests, however, recent estimates show that the annual damage by native species of insects is still greater. Table 2-5 shows the relative importance of native and immigrant insect pests, ranking them according to the amount of annual crop loss. The pests listed in the Table account for 75 percent of the total crop loss by insects. Native insects are responsible for a larger amount of the total losses than are the immigrant species: $956 million compared to $716 million. In addition, native insects occupy more of the higher ranks as pests than do the immigrant species. TABLE 2-5 RELATIVE IMPORTANCE OF NATIVE AND IMMIGRANT INSECT PESTS BY SIZE OF ANNUAL CROP LOSS Insect Annual Crop Losses ($ Millions) Native Pests Immigrant Pests Corn earworm 206 Boll weevil 201 European cornborer 158 Lygus bugs, cotton fleahoppers and other sucking insects (cotton and potatoes) 136 Grasshoppers 132 Bollworms 100 Tobacco budworms (native), hornworms (native) and green peach aphis (introduced) 100 Corn rootworm 92 Spotted alfalfa aphid 79 Green bug 62 Potato leaf hopper 50 Cutworms 45 Alfalfa weevil 41 Pea aphid 41 Hessian fly 28 Wheat stem sawfly 24 Fall armyworm 22 Corn leaf aphid 17 Apple mites 16 Cabbage looper (native) and cabbage worm (introduced) 16 Armyworms 14 Strawberry mites 13 Meadow spittle bugs 13 Brown wheat mite 12 Orange mites 9 Orange scale insects 8 Chinch bug 8 Mexican bean beetle 8 Southwestern corn borer 8 Onion thrips 7 Alfalfa seed chalcid 6 TOTAL LOSSES 956 716 SOURCE: USDA, ARS, 1965 Losses in Agriculture, Agriculture Handbook 291 5 DEFINING THE THREAT Given the record of establishment of immigrant species and the subsequent importance of many of them as pests, there is good reason to inquire about the additional foreign species that may be able to invade the United States. We need to establish the magnitude of the threat from invasion by additional foreign pests. On the other hand, given the large number of species and the low predictability for pest behavior among insects, as pointed out in the last chapter, is it meaningful to try to determine the precise nature of the threat? 31 THE THREAT OF INVASION There are perhaps 2,500,000 insect species, identified and unidentified, that are not present in the U.S. About 800,000 of these have been identified, and 6,000 of them are known to be damaging in foreign areas having ecological equivalents in the U.S. These relative magnitudes are illustrated in Figure 3-1. There are about 600 plant diseases and 20 animal discuses that may be considered significant. Some entomologists contend that the large potential for invasion, with its uncertainties, makes any attempt at ordering those foreign insect pests which are potentially most damaging to U.S. agriculture, totally misleading. The viewpoint of these entomologists is that there are hundreds of thousands of insect species abroad, and only a comparative handful of them are of economic significance. While most of the latter turn up on the lists of unwanted insects, they do not always live up to their reputations following arrival to their new environment. On the other hand, a number of the more serious introduced pests have come from that vast group of foreign pests whose potential for damage is unknown or not suspected. In other words, our ability to predict the consequences of the introduction of any given foreign insect is so poor that any list of allegedly injurious species would provide an inadequate basis for program decisions. The question boils down to this: how accurate do our predictions concerning the economic significance of particular foreign species introducible into the U.S. have to be before it makes sense to identify particular species to look for at ports of entry? A rational program for protection needs some notion of what species it is trying to keep out. Since it is faced with limited resources and cannot protect the nation against everything, it is useful to have some ordering of the potential invaders that provides an opportunity to make choices, however uncertain, in the use of program resources. A survey of the insect and other alien arthropod pests of potential danger to American agriculture has identified about 600 species that FIGURE 3-1 Foreign Insect Species in Perspective may be regarded as high risks. These are species known to attack, or to serve as vectors of diseases that attack, crop plants and livestock on which American agriculture and forestry depends. In addition to these species, there is a very much larger number, perhaps ten times as many species, that must be regarded as suspect. These are species having little economic importance because of the regulative action of specific natural enemies or because of agricultural practices that minimize their ability to develop injurious populations. All such species constitute a potential danger should they become established in the U.S. Past experience shows that many of our more serious insect pests are of this latter type. The Japanese beetle, spotted alfalfa aphid, and the cereal leaf beetle are examples of alien species that would not have been included in a list of pests known to have significant economic importance in their countries of origin. Many others could be added. Assuming then, that there are as many as 6,000 foreign insects and mites that are potentially dangerous to the United States and that only 600 of these can be listed by name, what are the prospects for the future? Obviously, total exclusion of all 6,000 is desirable, but experience suggests that this would be possible only at prohibitive cost, if possible at all. As long as commerce exists between the United States and other parts of the world there is a probability of establishment for each potentially dangerous species. The level of probability will be different for each species and may be affected by regulatory activities designed to exclude their entry. With the number of exotic insects and mites discovered over the past 480 years averaging a little over two per year, and the recent average of discoveries eight per year, as shown in Table 2-1, it is obvious that the probability of an exotic pest becoming established is very low. For example, assuming that an overall probability for each species might be as low as one percent (1%) and that establishments by the various species are independent, one should with high probability (99%) expect at least 43 new species to be reported as established in the United States each year. Actually, the rate at which exotic pests have recently been discovered (8 per year) would suggest an average probability between 0.04% and 0.22% at the 95% confidence interval. Although we are dealing with relatively small probabilities, we should not be misled into thinking that this implies a lack of importance. This is a situation where a 1% probability may be very high. To illustrate this point, Table 3-1 relates the probability of establishment to the time required before we would expect the pest to appear. TABLE 3-1 RELATIONSHIPS AMONG PROBABILITIES OF ESTABLISHING AN AGRICULTURAL PEST, AVERAGE PEST INFESTATIONS, AND AVERAGE YEARS UNTIL FIRST PEST INFESTATION* Probability of Establishment of an Agricultural Pest (Percent) Average Pest Infestations Per Year** (Number) Average Years Until First Pest Infestation*** (Number) 1 0.01 99.5 2 0.02 49.5 3 0.03 32.8 10 0.11 9.5 20 0.22 4.5 30 0.36 2.8 40 0.51 2.0 50 0.69 1.4 75 1.39 0.7 99 4.60 0.2 * An example of the interpretation of these numbers is as follows: If a pest has a probability of establishment of 20 percent, one would expect 0.22 infestations per year, and on the average one might expect the first infestation in 4.5 years. ** Assumes the arrival of infestations are described by a Poisson distribution. *** Reciprocal of the average infestations. The situation for plant pathogens is somewhat similar, recorded establishments averaging 3 per year over a 25-year period. From the listings of approximately 2,000 foreign plant pathogens 551 were chosen by the Task Force representative1 as posing significant risk to our agriculture. The selection of this 551 is influenced to a major extent by economic value of its host or hosts. We thus introduce an additional factor in the quarantine concept in that not only is the probability of entrance because of the nature of the pathogen considered but the possible economic impact; i.e., a pathogen of corn is of greater economic concern than one of geraniums. No consideration of the universe of fungi, bacteria, nematodes and viruses was attempted in this pest group. Some 50,000 parasitic and non-parasitic diseases of plants are listed as present in the "Index of Plant Diseases in the United States," Agr. Handbook No. 165, 1960. 32 THE VALUES AT STAKE In addition to the economic values at stake, the Task Force is aware that there are significant environmental and esthetic values which are threatened by exotic pests and diseases. Given the public concern about these values, the Task Force wondered what impact they might have on future quarantine and pest control policies. A sociologist, Dr. James H. Copp of the Economic Research Service, provided his views on the outlook for the social value of the environment. Because of the importance of this question, his statement is included in its entirety. 32.1 Outlook for Social Value of the Environment.2 How will people value the environment in the future? Although there is little concrete evidence to go on, it is possible to make some "informed guesses" that may be helpful in framing pest and disease control policy. First of all, I think we will have to admit that environmental concerns are here to stay; they are more than a passing fad. Granted, there has been considerable fadism and much dissatisfaction with the social order in general displaced on environmental problems. The environmental issue has provided a convenient outlet especially for those youth who couldn't deeply identify with the problems of poverty or those of the blacks. Black activists have been particularly unhappy about the competition from the environmental movement and the way it has dissipated support of middle and upper class whites from their cause. The outlet-for-dissatisfaction interpretation is also supported by the observation that few blacks are involved in the environmental issue; they have a vital cause 1. C. H. Kingsolver, with assistance from C. G. Schmitt and K. R. Irish, PDRL. Particular thanks to R. W. Beardmore, APHIS, Dr. Magan Golden and Mrs. Virginia Harrington, Plant Nematology Laboratory, Bernard Lipscomb, Mychology Laboratory, ARS, and Dr. Keith Shea and Staff, Forest Disease Research, U.S. Forest Service. 2. This section was prepared by Dr. James H. Copp, now at the Department of Sociology and Anthropology, Texas A. and M. University, College Station, Texas. much more near at hand. The environmental issue also has the attraction of being safer and more "proper" than protest against the Vietnam War, which carries an implication of disloyalty and support of the enemy. Thus the environmental issue provides a much more legitimate and constructive outlet for the free-floating dissatisfaction of American youth and adults with the existing order. Going beyond the ephemeral attractions of the environmental movement as an outlet for youthful dissatisfaction, the environmental concern is here to stay. It is here to stay because the environmental problem is rooted in the development of our economic and social system. It is a direct consequence of the pressure of people on the environment-—a pressure based both on expanding numbers and a high level of economic development which consumes monstrous quantities of natural resources. We have come to a point in our economic development where the trade-offs between the quality of the environment and economic growth are becoming more obvious to and more demanding of the public. The paradoxical thing about economic development is that it provides more people with the income levels and the leisure to appreciate the natural environment esthetically. Thus, at the very time our economic growth most threatens the existing environment we have arrived at a point where we treasure the natural order on a mass basis. As a result of these tendencies, rooted in developments of our social and economic system, I do not see our concern with environmental issues decreasing. As the pressure to degrade or alter the environment increases, I see the conflict over environmental issues increasing because the tradeoffs are going to become more costly for both the environmentalists and the economic development forces. However, I think it is important to make some distinctions in environmental concerns. The public is most concerned about the pressures from economic exploitation and pollution. It is seen as a zero-sum game with heroes and villains. Here the "bad guys," the economic exploiters, are seen as profiting at the expense of the public and the environmentalists, the "good guys." The environmentalists see the issue as competition in which the exploiters are taking resources which the environmentalists feel are in the public domain, and hence for the use of all. I feel the situation with regard to pest and disease control is usually somewhat different. Pest control is seen as a good thing. If pest control preserves the natural ecosystem it is good. Further, if success or failure in controlling pests disturbs the ecosystem, yet no group is seen to profit from the results, I suspect there will be relatively little uproar. I think the environmentalists are most concerned by those occasions wherein man disturbs the balance of nature to enrich some group at the expense of others. The real conflict in the environmental issue is one of the distribution of rewards. The environmentalist gets rewards from his esthetic and contemplative enjoyment of nature; he objects to the competition from resource exploiters who want to use nature for economic rewards. Therefore, with the environmental issue continuing on the national agenda for the foreseeable future, I see a latent resource of good will supporting pest control as a positive force preserving the balance of nature. However, if pest control fails to protect a species I see relatively little uproar so long as no group is seen as profiting from this dislocation and no agency is found to have been derelict in duty. On the other hand, the social prognosis is not clear at all if positive measures in pest and disease control by man have side effects that endanger other species. The conflict will be most bitter if it is clearly apparent that some particular group, rather than the public as a whole, benefits from the control of the original pest. The pest controlling agency itself will become embroiled in the conflict as the scapegoat for the "blunder." Politicians looking for an issue to exploit will be attracted. Here about the only defense is improving the public's understanding of the interdependence of nature and of the impossibility of accurately predicting all the consequences so that the failure will be more likely attributed to ignorance (lack of scientific knowledge) than incompetence or willful malfeasance. The complexity of the problem and the contingency of error should be stressed in justifying research funds. There is presently no good way of accurately predicting how the public will react to the trade-off of controlling one species at the cost of endangering another, particularly when benefits to private groups are unclear. Evaluation will have to proceed on a case-by-case basis. We have to recognize that certain species attract more concern from the public than others, we have our totems and we have our "varmints," wrong as the public may be about the nature of ecological balance. For instance, bald eagles may be over-valued, snakes and skunks under-valued. At times, though we may dislike the practice in principle, public opinion polls may be necessary in order to determine what kind of controls are politically feasible. It is regrettable fact that many of the decisions about pest and disease control are going to be made in the political arena. There are genuine conflicts of interest that are not clearly resolvable on the basis of scientific evidence. The scientist is not the ultimate one who resolves conflicts over the distribution of rewards and costs in a society. 32.2 The California Model. In California, the Department of Food and Agriculture has developed a model for ranking those pests that are not established in the State. This was done as part of an assessment of California's plant quarantine program. Each pest was given a numerical score based on the following set of values: Economic Impact (Includes damage and additional costs) 0 - No effect (Less than $100,000) 1 - Minor effect ($100,000 to $1,000,000) 2 - Major effect (More than $1,000,000) Social Impact 0 - Affects up to one million persons 1 - Affects one million to five million persons (25% of California's population) 2 - Affects more than five million persons Environmental Impact 0 - No effect 1 - Loss limited to damage only 2 - Loss of one or more species Under this scheme, the higher the numerical score, the more dangerous the pest. This model has the virtue of explicitly considering a wide range of values, which seem appropriate in a public program. It gives important weight to social and environmental impacts, rather than focusing entirely on those values determined in the market place. Two shade tree diseases not established in California, Dutch Elm Disease and Oak Wilt, were among the pests at the top of the list, whereas many of the traditional agricultural threats were rated lower, because their impacts were primarily economic. 33 THE MODEL FOR RANKING IMPORTANCE 33.1 The Conceptual Design. The Task Force considered the desirability of including social and environmental values in the model. However, in this first attempt at ranking it was decided to use only the economic values, since these are quantified and readily available and the use of a single scale of values would simplify the model. The ranking of pests might be quite different, as in the California Model (Section 32.2), if other kinds of values were incorporated. A three-step procedure was developed for ranking exotic pests. First, estimate the probability of specific exotic pests becoming established in the United States. Second, evaluate the economic impact if those pests became established. Third, multiply the first value times the second; that is, the probability of an exotic pest becoming established times the economic impact of the pest if it becomes established. This value constitutes the expected score of economic importance of exotic pests in the U.S. and was labeled Expected Economic Impact (EEI). ("Expected" is used here in the statistical sense; i.e., "average" or "mean.") in algebraic terms, EEI = P x E Where EEI = Expected economic impact. P = Probability of Pest becoming established in the U.S. during the next year. E = Economic impact if pest became established. The conceptual importance of this procedure is that it yields a quantifiable measure of economic risk. One important limitation of the model is that it is static rather than dynamic. For example, the rate of spread of an immigrant species through its ecological range is not taken into account. This is a significant time-related variable. However, the Task Force excluded it from the model, believing that the estimates required would have a wider confidence interval than the other variables in the model. There is an urgent need to obtain estimates of rates of spread for important pests in their overseas locations, in order to provide a basis for estimates of spread in the U.S. Obviously, the rate of spread for animal diseases is quite different than that of the insects and plant pathogens. A brief description of how estimates were derived for the probability of a pest becoming established in the U.S. and the economic impact if a pest became established follows in Sections 33,1 through 33.4. A fuller and somewhat more technical description, prepared by Dr. Bert Levy of the Task Force, follows in Sections 33.5 through 33.7. 33.1 Probability of Pest Becoming Established. It was assumed that the probability of a pest becoming established was related to the volume of vector material imported into the U.S., hitchhiking potential of the pest, and the ease with which a pest becomes established after arrival. It was felt that impressions of the relationship could be estimated empirically with a second degree equation for the general relation. P = G (f1, f2, f3) Where P = Probability of pest becoming established, f1 = Volume of vector material imported into the U.S. f2 = Hitchhiking potential of the pest. f3 = Ease with which a pest becomes established after arrival. 33.2 Economic Impact If Pest Became Established. The economic impact of an agricultural pest if it became established is used here as a marginal measure. It is the expenditures required to maintain production of the host crop. It is the summation of the added cost of pest control on old units, plus the added cost of pest control on new units needed to maintain production, plus the added cost of raising the new units. The formula used is: E = VRT + V (URT ) + W (URT ) 100-U 100-U Where: E = The economic impact of the established pest. R = The amount of the host grown. T = The ecological range of the pest as a percent of the range of the host. U = Percent loss in yield when normal controls are used. V = Added control cost per unit per season for the pest. W = Variable cost per unit for host. Amount of money required to increase growing area by one acre, herd by one head, etc. 33.3 Assembling the Information. In order to calculate the economic impact if a pest became established and to estimate the probability of a pest becoming established, the following information was assembled: 1. Countries or regions of the world presently infested. 2. The most important host materials. 3. Ecological range of pest in the United States as a percentage of the range of host crop. 4. Hitchhiking potential, ignoring quarantine programs. 5. Ease of colonization once pest has arrived. 6. Percent loss in yield in the United States for affected crops with expected methods of control. 7. Cost per acre per season of a normal pest control program needed for crops affected by this pest in the United States. Include cost of materials and application. 8. Probability of pest becoming established in the United States. 9. Level of host material shipments from an area where pests exist to areas in the United States where pests could become established. 10. Total acres of affected crops. 11. Variable cost per acre for crops affected. 12. Average yield of affected crop. Table 3-2 provides some examples of the kind of information that was assembled for each pest. The world regions are listed in Table 3-3 and outlined on the map, Figure 3-2. These areas are the world trade areas of the U.S. Department of Commerce, and statistics on the importation of agricultural commodities from each of these regions are available. A listing of 171 crops and animals, together with estimates of the variable cost per acre or per animal unit was assembled for use in developing the EEI score. Table 3-4 provides 19 items from this list of hosts as an example. 33.4 Explanation of Computer Documents. (These documents appear as appendices) Computer Outputs There are several computer listings which detail or summarize the information assembled about agricultural pests. Most of them are self-explanatory. Ranking by Relative Risk This listing is presented as a bar chart. The bar represents a 75 percent confidence interval for the "Expected Economic Impact" of the agricultural pest. The pests are listed in descending order of the upper end of the confidence interval. The lower end of the chart is zero millions of dollars. The upper end is 500 million dollars. Any value above 500 million has been truncated to 500 million. The upper end of a bar may be viewed as an estimate of the economic impact likely to be incurred if the pest were to become established. The length of the bar is a measure of the quality of the estimate. A short bar indicates a reliable estimate. A longer bar indicates a less reliable estimate. Basic Input Data The pests are listed alphabetically. Each pest is listed once for each host with which it is associated. There is an additional summary line, indicated by host 999. This line includes a total economic impact estimate, the sum of the estimates over the various hosts. The parameters previously discussed are identified and listed. TABLE 3-2 EXAMPLES OF THE INFORMATION ASSEMBLED FOR USE IN THE RANKING MODEL OF ALL SIGNIFICANT EXOTIC PESTS Pest or Disease Expected No. of Years Until First Infestation Regions of World Infected Host Materials Pest Range as a Percent of Host Range Hitchhiking Potential Ease of Colonization Added Control Cost Percent Yield Loss Animal Diseases: Foot and Mouth Disease 0.5-2.0 3,4,8,9, 11,12,13, 14,15,16, 17,18,19 All cloven footed animals 100% High High Cattle $1.80 Swine $2.66 25% Nairobi Sheep Disease 5-10 12,20 Sheep Goats 75% High Medium Quarantine Control $0.25 40% Teschen Disease 5-10 8,9,10 16,19,20 Swine 100% Low Medium Quarantine Control $0.25 25% Plant Diseases: Helicobasidium mompa (violet root rot) 5 15,16 104 species in 45 families and 76 genera 100% High High $20 20* Rosellinia quercina 4 8 hardwoods conifers 100% High High $7-12 <5% Sclerospora phillipensis (downy mildew) Insects; 6 16 corn sorghum teosinte 70% Medium Medium $10-15 40% Ceratitis capita ta - 9,11,13 14,16,17 18,20 citrus, pear peach, apricot 30% High High $20 5% Melanogromyza phaseoli - 12,13,16 17,18,20 beans,including soybeans 30% Medium High $5 5% Trogoderma granarium - 8,9,11,12 13,14,15,16 17,18,19,20 stored grain 100% High High - 5% TABLE 3-3 WORLD REGIONS 1. U.S.A. 2. Canada 3. Eastern South America 4. Western South America 5. Caribbean 6. Central America 7. Mexico 8. Northern Europe 9. Mediterranean Europe 10. United Kingdom 11. North Africa 12. Developing Africa 13. Republic of South Africa 14. Middle East 15. Japan 16. East Asia 17. South Asia 18. Communist Asia 19. Communist Europe 20. Oceania TABLE 3-4 SELECTED EXAMPLES FROM THE LIST OF CROP AND ANIMAL ESTIMATES USED TO COMPUTE THE EEI SCORE Crop or Animal Acres, Trees, Vines, Plants, or Animal Units (thousands) Variable Cost Per Unit (dollars) Alfalfa 27,814 19 Almonds 205 439 Apples 600 450 Apricots 41 574 Artichoke 9 587 Ash 9,153 515 Asparagus 139 479 Avocados 2,118 3 Azalea 32,000 1 Barley 9,388 13 Beans - dry edible 1,481 52 Beans - green lima 83 876 Beans - snap 328 285 Beech 8,076 515 Beets - sugar 1,575 106 Birch 6,370 515 Blackberries 8 1,250 Blueberries 43 1,530 Cattle 96,669 244 33.5 Mathematics of the Ranking Model. (Those readers who are not mathematically inclined are invited to skip to Section 4 for a presentation of some of the results of the ranking procedure employed by the Task Force.) A discussion of the "Proper" methodology for comparing the importance of foreign agricultural pests will be almost completely avoided here. Possible ranking criteria include economic, environmental, political and emotional factors. Little scientific information exists on these points and choices among models and criteria are necessarily subjective. A description of our approach follows, along with some rationalization of our choices. The criterion selected for ranking the agricultural pests is "Expected Economic Impact" of the pests on U.S. agriculture. The quantification of economic impact is the expenditures required to maintain agricultural production in the presence of the pest. The word "expected" is used in the statistical sense since some of the quantities in the model are random. A simplified picture of the model which contains most of the ideas can be presented in an example. Consider a hypothetical agricultural pest not presently in the U.S. To simplify terminology we will assign him the common name "Sam." Sam is known to attack grains (wheat, rye, oats, and corn). Sam's economic impact on these crops are respectively fifty (50), eight (8), five (5), and twenty (20) million dollars. The probability that Sam will establish himself in this country within the next year is 0.02, two chances in a hundred. Sam's expected impact on U.S. agriculture is then: The general formula expresses the relationships symbolically, (EC)i is the expected economic impact of pest i. Pi is the probability that pest i will become established in the U.S. in the next year. (EI)ij is the economic impact of pest i on crop j. The summation extends over all crops upon which pest i has significant adverse effect. Formula (1) is not directly usable. The probabilities Pi and the economic impacts (EI)ij are unknown. The latter problem has been conveniently avoided. It is our consensus that the errors made in ascertaining the economic impacts, (EI)ij are much smaller than those made in estimating the probabilities Pi. Therefore, as a practical matter, we assume the former quantities to be known exactly. Our problem is then determining estimates of the probabilities. The number of pests under investigation is large. It is unreasonable to expect even the most knowledgeable biological scientists (entomologists, plant pathologists and veterinarians) to be able to ascertain the values for any sizable portion of the pests. It was hoped that the probabilities were roughly predictable from some underlying factors which were observable. This seems to be the case. The underlying factors upon which we rely are: 1. Volume of vector material imported into the U.S. (f1)j 2. Hitchhiking potential of the pest. (f2) 3. Ease with which pest will establish itself after arrival. (f3) It was necessary to quantify these factors. Each factor is assigned the value l(low), 2(medium), or 3(high). The values are used in equations to obtain a pessimistically high estimate, Pi, and an optimistically low estimate, Pi, for the probability Pi of pest i becoming established. The estimates satisfy the relation: The methodology used to obtain these is discussed later. These estimates may now be used in place of Pi in formula (1), (2a) (2b) This gives us a pessimistic estimate, (EC)i and an optimistic estimate, (EC)i, of the economic impact of pest i. The difference between those two estimates, (EC)i - (EC)i is a measure of the degree of certainty in the estimation. A small interval indicates a close estimate, while a large interval indicates a great deal of uncertainty. The pessimistic estimate, (EC)i, is used to rank our list of agricultural pests. The length of the prediction interval is included as a bar graph to indicate the uncertainty in estimation. The results appear as an exhibit at the end of this article. In the sections which follow, it will be seen that our procedures proved to be reasonably good. There is one class of pests, forest pests, which are a notable exception. The procedures tend to rank them too high. We surmise that this is caused by the trichotomization of the variable, ease of establishment, in the model. Virtually all of these pests are rated low in this attribute. The model is not sensitive enough to indicate how extremely low this attribute should be rated. 33.6 Predicting Probability of Establishment. It was hypothesized that "the probability of establishment Pi would be simply related to three underlying factors. The first factor is the quantity of vector material upon which pest i can travel that is imported into the United States. The second factor is the hitchhiking potential of the pest. The third factor is the ease of colonization of the pest once it has arrived. Each factor is treated as having three levels, low (=1), medium (=2), and high (=3). Thus, the quadratic predictive model for pest i is: Each of the quantities [fji] take on one of the values 1, 2, or 3 as is appropriate for pest i. Confidence Intervals Computations This listing is in two sections. The first section covers plant pathogens, pests assigned identification numbers less than 1000. The second section lists insect pests, pests assigned identification numbers greater than 1000. The sections are subdivided according to host with the artificial summary host 999 listed last. In each subsection, pests are listed in descending order of expected economic impact. The listing includes point estimates of the expected economic impact and probability of establishment of the pest. Fifty (50), seventy-five (75), and ninety (90) percent confidence intervals are included for each of these parameters. Host Number Index This index appears ordered numerically by the numbers assigned to the various hosts and alphabetically by host name. The two fields of numerical data are the ones previously designated R and W, respectively. The coefficients, m, a, b, c, d, e, and g, were estimated using the least squares procedure. The estimation was performed twice--once for insect pests and again