Hawaiian Ecosystems at Risk project (HEAR) Control methods for ants

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Overview

It is important to determine the identity of the ant species present before an ant management program can be initiated, because ant behavior, biology, and ecology vary among species. Control strategies must be developed which are appropriate for the specific ant species. Ants are easier to control when the colony is small and localized. Eradicating recent infestations is the best strategy.

Some ant species (e.g., Hypoponera opaciceps) may be present but will never cause any significant problems to the environment, mainly due to the small colony size. No attempts at controlling such species may be needed. Other species can cause serious problems and should be controlled, such as the big-headed ant (Pheidole megacephala), the Argentine ant (Linepithema humile), the long-legged ant (Anoplolepis longipes), the tropical fire ant (Solenopsis geminata), Solenopsis papuana, and the black house ant (Ochetellus glaber). These ant species build large populations of interconnected colonies, occupy acres of land, and dominate the environment. Control of these ants is essential to prevent the decimation of the native fauna and flora.

Control of ants in natural habitats is often difficult and problematic. Reasons for the difficulty in ant management in natural habitats include 1) terrain; 2) undesirable effects of Control methods for ants on non-target organisms; 3) abundance of naturally occurring food; and 4) changes in food preferences due to ant developmental stages.

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Terrain

Ants often occupy extensive areas of rough or inaccessible terrain. It may on occasion be difficult or impossible to gain access to these areas by foot. The result is that it can be quite expensive just to get to the infested area, let alone attempt to control the ants.

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Undesirable effects of Control methods for ants on non-target organisms

Control methods for ants could have equal or more severe deleterious effects on the native fauna in the area. Therefore, the use of a control method which is ant species specific is preferred. The use of insecticide-laden baits is ideal in these situations. Baits can be formulated to be attractive to ants, yet unattractive to the majority of native arthropod species. Under specific situations, baits can be offered in bait stations to minimize the impact on the native fauna. This is in contrast to other ant control techniques, such as insecticidal sprays, which are not host specific. Although sprays work well for ant control in some urban situations, they are not practical for naturalized areas because of non-target effects.

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Abundance of naturally occurring food

The main difficulty with baits is that ant colonies often have a plentiful and varied diet available to them in natural areas, and the ants may not be interested in or attracted to the bait offered. Food preferences will change depending on which foods are naturally available in the environment. Naturally occurring food will change seasonally. For example, protein foods are less plentiful in the winter months, but more common in the spring and summer months when insect populations increase. Carbohydrate sources also are more plentiful when the vegetation is flowering (available as nectar), although certain ant species are known to tend Homopteran insects for the honeydew they produce year round.

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Changes in food preferences due to ant developmental stages

Food preferences of ant colonies will also change due to ant developmental changes in the colony. For example, egg, brood (larvae and pupae), and worker production increases in Argentine ant (Linepithema humile) colonies in the spring months at Haleakala National Park (Krushelnycky and Reimer, unpublished). Increases in the production of eggs and worker ants will increase the protein requirements of the colony. During this time, baits with protein attractants are much preferred by this ant over carbohydrate or oil based baits. Later, the colonies shift to a preference for carbohydrate based foods in the late fall. At that time, the production of alates (winged reproductive forms of the ant) has ceased and the production of eggs and workers has decreased. The carbohydrates are still required, however, for the remaining workers in the colony.

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Baits

A number of baits are being developed which contain various attractants, but the majority of baits are directed towards the urban ant pests and a few agricultural pest species. In general, insecticide laden baits are the preferred method for management of pest ants in natural areas. They have the advantages of being easily applied over large, inaccessible areas, and being relatively host specific to the target ants. Different baits have different attractants so that they are attractive to specific ant species. For example, the bait Amdro contains soybean oil as an attractant and is readily fed upon by the big-headed ant (Pheidole megacephala). The granular baits Maxforce and Combat contain insect proteins as an attractant. These baits are attractive to Argentine ants (Linepithema humile). Both of these baits have been tested in natural areas and large agricultural acreage with various results. It is always a good idea to test a small amount of the bait to test whether the ants will carry it back to the nest, before committing to a large-area control program.
  • Amdro
    Amdro has proven to be very effective against the big-headed ant (Pheidole megacephala) in abandoned pineapple fields. Applications at 1.5 pounds/acre has given 100% control. Although no trials of this bait have been conducted in forested areas, it would seem to be a excellent candidate for testing. The abandoned pineapple fields contained an abundance of alternative food sources, yet Amdro was readily accepted by the ants.

  • Maxforce
    Trials at Haleakala National Park have demonstrated the effectiveness of Maxforce against the Argentine ant (Linepithema humile). Although 100% ant control was not achieved when Maxforce was applied at the rate of 2 pounds/acre in native scrubland at 6500 feet, the ants were reduced significantly. Typically, a reduction in ant numbers of 80-95% was observed within one week after treatment. The numbers of ants remained low at 70 to 89% below pretreatment levels two months after treatment. Maxforce may have greater effectiveness if applied at a time when the ants are at a peak in their acceptance of protein food sources. Maxforce should work very well at managing small localized ant populations. Maxforce may also be effective in maintaining a buffer zone to prevent ant movement into areas particularly sensitive to ant invasion.

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References

Romero, Hernan, and Klaus Jaffe. 1989. A comparison of methods for sampling ants (Hymenoptera: Formicidae) in savannas. Biotropica 21(4): 348-352.

Medeiros, A. C., L. L. Loope, and F. R. Cole. 1986. Distribution of ants and their effects on endemic biota of Haleakala and Hawaii Volcanoes National Parks: a preliminary assessment. Proceedings of the Sixth Conference in Natural Sciences, Hawaii Volcanoes National Park. Cooperative National Park Resources Studies Unit, Department of Botany, University of Hawaii, Honolulu, Hawaii, USA.

Perkins, R. C. L. 1913. Introduction. Fauna Hawaiiensis 1(6): i-ccxxvii(xli-xlii).

Romero, Hernan, and Klaus Jaffe. 1989. A comparison of methods for sampling ants (Hymenoptera: Formicidae) in savannas. Biotropica 21(4): 348-352.

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The Hawaiian Ecosystems at Risk project (HEAR) is currently funded by grants from the Hau'oli Mau Loa Foundation and the U.S. Forest Service with support from PCSU (UH Manoa). Historically, HEAR has also received funding and/or support from the Pacific Basin Information Node (PBIN) of the National Biological Information Infrastructure (NBII), PIERC (USGS), the USFWS, HCSU (UH Hilo), and HALE (NPS).
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Technical details in the main text of this page were last updated on 04 July 2007 based on information provided by Neil Riemer (Hawaii Department of Agriculture). This page was created on 04 July 2007 by PT & LF, and was last updated on 04 July 2007 by PT. Valid HTML 4.01!