A Message from the Vet - July 2010
Invasive Species Control: Strawberry Guava

Hawaii boasts a beautiful and unique ecosystem which serves as a habitat for native and invasive species alike. The modern-day increase in global traffic has resulted in a breakdown of the natural barriers that have previously maintained indigenous species within continental regions and island ecosystems. Invasive alien species have been introduced to Hawaii both purposely and inadvertently, contributing to the remodeling of Hawaii's ecosystem, reduction of its unique biodiversity, and extinction of many native species. The agriculture industry, horticulture industry, pet trade, cargo transportation, and human travel all serve as vectors to transport non-native species into Hawaii.

While non-native species do not necessarily acquire invasive characteristics, invasive alien species are defined by spreading rapidly and reducing the populations of native species in the areas in which they spread. Invasive species are a concern to Hawaii's already threatened native species because they may compete for resources such as food or shelter, prey directly upon native species, or interbreed with native species.

In the case of the invasive strawberry guava plant, the Hawaii Department of Agriculture is currently proposing a form of biological control by release of a non-native insect from Brazil in the hopes that it will control the plant's spread. Unfortunately, there is no way to ensure that the non-native insect will not take on invasive characteristics in Hawaii's ecosystem. No research can guarantee that the non-native insect will target only the strawberry guava plant and leave our other native or agriculture plants alone. With our unique ecosystem, there is little room for experimentation and failure with biological control.

While biological control measures have worked in a sparse handful of scenarios, and appear desirable because they operate without much human intervention after the initial introduction, these measures typically fail to control the target species, and often spin off to affect a myriad of other ecological facets that were not previously considered. Will the insect find Hawaii's other flora easier targets than the strawberry guava? What will the insect feed on if strawberry guava is eradicated or population decimated? Do we have the appropriate predators to keep the invasive insect population under control? Extensive host-testing and release of only narrowly host-specific species may reduce this risk, but particularly in Hawaii, the failure of this endeavor is evident in its history of introduction of notorious alien species such as the mongoose and cane toad.

I believe Hawaii's ecosystem is too valuable and fragile to serve as another biological control experiment. The cost of failure is too high. We could easily be trading one invasive species for two invasive species. As an alternative to introducing more non-native species to the islands, many introduced species can be controlled at low densities. For example, invasive plants have been controlled with manual and herbicide control in Florida, and the Alberta Rat Patrol maintains low populations of Norway rats through anticoagulant baits and hunting tactics. Informing and involving the local community in managing the invasive population are keys to long-term successful solutions. The best management of invasive species is always prevention. Our primary focus should be on the development of continuous ecosystem management programs to prevent the introduction of these non-native species, rather than belated responses to already established invasive species.

Jill Yoshicedo, DVM

Photo of strawberry guava on homepage courtesy of www.nps.gov.

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