Strawberry guava biocontrol
Frequently-asked questions (FAQ)


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Questions addressed in this FAQ:
Why is strawberry guava a problem?
Aren't there methods to control strawberry guava by hand? Why do we need biocontrol?
Why was this bug chosen to control strawberry guava here in Hawaii?
How will the bug help to control strawberry guava?
How do we know that the strawberry guava bug won't hurt other plants?
Isn't this bug likely to adapt to feed on other plants over time?
Won't strawberry guava be replaced by something worse?
Don't native birds depend on the fruit?
How can I protect trees in my own yard from the strawberry guava bug?
Many people use the wood and fruits of strawberry guava. How will those uses be affected?

Q. Why is strawberry guava a problem?

A. Strawberry guava was imported from Brazil and has spread out of control on all the major islands in Hawaii where it has no natural predators to keep it in check. Not only does it spread rapidly, but it also grows in dense stands crowding out other plants and destroying habitat for nesting birds and native insects. A forest invaded by strawberry guava also means a loss of water. Studies have shown that 27-53% of water is lost, which is a precious resource for our drinking water and farms. Also, strawberry guava provides a huge reservoir for damaging fruit flies, which is an additional threat to local agriculture.


Q. Aren't there methods to control strawberry guava by hand? Why do we need biocontrol?

A. Yes; however, only small patches can be managed in this way. For many years, people have worked to control strawberry guava by cutting stems and using herbicides. Over hundreds of acres, these methods become extremely expensive and difficult, especially on rough terrain and in remote areas. Also, strawberry guava resprouts easily, so repeated treatments are needed over many years. Introducing a natural predator (a biological control, or "biocontrol" organism) of strawberry guava would be integrated into a holistic approach to help bring balance to our forests by keeping strawberry guava in check.


Q. Why was this bug chosen to control strawberry guava here in Hawaii?

A. Currently, strawberry guava has no natural predators to keep it in check in Hawaii. This bug, Tectococcus ovatus, was selected after many years of research showed that it is both safe and effective. Studies in Brazil show that this bug feeds only on strawberry guava, causing reduced growth and seed production. Extensive testing of over 80 native, commercial, and ornamental species demonstrates that this bug will not affect any other species in Hawaii.


Q. How will the bug help to control strawberry guava?

A. Young Tectococcus ovatus bugs settle and feed on newly sprouted leaves of strawberry guava and cause the leaves to form growths called galls. Because the plant puts energy into forming galls; it doesn't put as much energy into growth and fruit production. The natural predator helps to naturally slow it down. Hawaii's native plants have native bugs that help to keep them in check in similar ways. The strawberry guava bug will not kill the plant but will just slow its rapid growth and regeneration so that other plants have a chance.


Q. How do we know that the strawberry guava bug won't hurt other plants?

A. Observations in Brazil and rigorous testing demonstrate that this bug is specialized to feed only on strawberry guava and poses no threat to other plants in Hawaii. It won't even feed on strawberry guava's nearest relative in Hawaii, the agriculturally grown common guava (Psidium guajava), which is also native to Brazil. Even when they grow side by side, the strawberry guava bug, Tectococcus ovatus, does not jump. The strawberry guava bug has never been recorded as a pest of any agricultural or ornamental plant. Detailed studies over the last 15 years have shown that native Hawaiian and introduced plants in the same family as strawberry guava--ohia, mountain apple, and jaboticaba, among others--will not be affected by the bug.


Q. Isn't this bug likely to adapt to feed on other plants over time?

A. No. In its native range in Brazil, Tectococcus ovatus is exposed to a great diversity of plants including hundreds of species in the same family as strawberry guava, but the insect is found only on two species of strawberry guava (one of which is not present in Hawaii). The evidence from its native range indicates that this bug has not adapted to feed on other species in many thousands of years. Adaptation to feed on new plants is extremely unlikely for a gall-forming bug because it has such a close relationship with its host. If the strawberry guava population declines, the strawberry guava bug population also declines since it is entirely dependent on the plant.


Q. Won't strawberry guava be replaced by something worse?

A. This is unlikely. This bug reduces the vigor of strawberry guava, but does not kill trees. There will be no widespread die-off of strawberry guava that might expose watersheds or open the forest to the spread of other invasive plants. Reduced vigor of strawberry guava will just give native species a chance to grow and spread. By slowing regeneration of strawberry guava where it is removed by cutting, this bug will help us to restore forests with native species.


Q. Don't native birds depend on the fruit?

A. No. Non-native birds, pigs, rats, and insects eat strawberry guava fruit, but native birds depend primarily on native Hawaiian plants and insects for their food. Strawberry guava destroys native forest habitats, reduces the abundance of native plants, and provides little in the way of insect food for birds. Because of its ability to degrade native forests, strawberry guava is considered one of the greatest threats to endangered forest birds on all the main Hawaiian Islands.


Q. How can I protect trees in my own yard from the strawberry guava bug?

A. This bug has limited dispersal ability, so property owners are unlikely to see effects on their trees for many years. Homegrown strawberry guava trees could be protected by spraying organic horticultural oils commonly used on fruit trees to control existing pests.


Q. Many people use the wood and fruits of strawberry guava. How will those uses be affected?

A. The strawberry guava bug will not eliminate strawberry guava. There will still be plenty of strawberry guava. The bug will only reduce its vigor and spread. Wood will continue to be abundant. Fruit will still be common when in season, but it will not be at the damaging levels that it is now in forest areas.



The Hawaiian Ecosystems at Risk (HEAR) project is currently funded by the Pacific Basin Information Node (PBIN) of the National Biological Information Infrastructure (NBII) through PIERC (USGS) with support from HCSU (UH-Hilo). More details are available online. Pacific Basin Information Node (PBIN)National Biological Information Infrastructure (NBII)

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