Biological control: Nature’s pest management

Farmers on Kauai produce a great diversity of agricultural commodities, but every crop is attacked by one or more kinds of pests, which are usually alien species that arrived in ships or planes. These invasive species pose a continuous and severe challenge to island farmers.

One reason that invasive species are so damaging is that the predators, parasites and pathogens that attack the invaders in their native land do not exist here. Without these natural enemies to keep things in check, pest populations can explode.

Biological control seeks to re-establish nature’s balance by importing natural enemies that evolved with the pests overseas, and establishing them in the islands where they can carry out their natural roles.

Biocontrol is a time-tested method that is generally safe and cost effective. Hawaii has one of the best records in the world for successful biocontrol of insect and weed pests. Some of the species controlled include stinging nettle caterpillar, banana skipper and coconut scale. Biocontrol of pamakani weeds alone is estimated to have had an economic benefit surpassing $100 million.

The cost:benefit ratio of biocontrol is often more favorable than that of other pest control methods. Chemical companies spend millions for registration of a single new insecticide. Even when an effective chemical is found, it must be purchased and reapplied by farmers every year. With self-replicating biocontrol agents, once an initial release is made the organisms can reproduce in the field and spread on their own. Pest control continues without further expenditures.

Some have expressed concern that biocontrol agents might have negative environmental impacts. Problems cited usually refer to vertebrates (like the mongoose) and snails that were imported before strict importation rules were in place. However, recent introductions that have passed through strict state and federal quarantine procedures have a very good safety record. Mandatory permits and a rigorous review process help ensure that only natural enemies that are safe are released.

Several factors will make biological control an increasingly important component of pest management for Hawaii in the future.

First, the rate of invasion by pest species is growing with increasing levels of trade and military transport through the islands.

Second, the federal Food Quality Protection Act will lead to withdrawal of some insecticides currently available for farms. Third, increased levels of pesticide resistance among pests, and urbanization near farm boundaries will lead to continued loss of chemical options. Biological control stands poised to fill this gap, but faces some obstacles of its own.

It is difficult to profit from self-replicating natural enemies; therefore, there is little private investment in biocontrol research and implementation.

Publicly funded agencies can do this work, but in recent years both CTAHR and HDOA have lost staff due to budget cutbacks. Biocontrol practitioners face a daunting bureaucratic gauntlet when they try to obtain permits for release of natural enemies. Permit requirements are extremely stringent, and red tape can lead to extensive (and costly) delays.

Also, the state has a shortage of licensed quarantine facilities necessary to ensure safe containment of new agents.

Despite these obstacles, biological control work in Hawaii continues. For example, a recent cooperative project between HDOA and CTAHR scientists led to the successful control of an insect that threatened wiliwili trees, a keystone species in native lowland forests.

Biological control does not work in every situation, but when it does … it is often the best, and sometimes the only pest management option available.

For more information or questions, contact the UH-CTAHR Extension office in Lihue.

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Dr. Russell Messing is a researcher and county administrator for University of Hawaii College of Tropical Agriculture and Human Resources. Do you have a plant, garden or invasive species question? Contact the CTAHR Extension Office at 274-3471 or stop by the office in the State Building at 3060 Eiwa St., Room 210, Lihue. The Plant Clinic (for plant insect, disease and soil problems) is open every Monday, 8:30-11:30 a.m.

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