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Selecting the Perfect Insect Pest

Media Contact:
Jennifer Martin, (202) 720-8188

By Stacy Kish, CSREES Staff
August 1, 2008

The weevil (Ceutorhynchus scrobicollis) may be the biocontrol answer to invasive garlic mustard.
Credit: Harriet Hinz and Esther Gerber

America's forests are under attack, but scientists believe the careful release of insect predators may effectively control the invasion.

Garlic mustard (Alliaria petiolata) has become an invasive species spreading throughout temperate forests across the United States. This plant is choking out native plants on forest floors and threatening ecosystem diversity. With funding from USDA's Cooperative State Research, Education, and Extension Service, an international group of scientists created a computer model to predict the perfect insect predators for this invasive plant.

Adam Davis and colleagues at University of Illinois, Michigan State and Cornell University tackled this issue along with the Commonwealth Institute of Biological Control in Switzerland. The scientists believe the introduction of the perfect pest, in combination with quarantined research tests, will help reduce the garlic mustard population.

"The traditional method (of eradication) was to release multiple agents into the environment to overwhelm the pest," Davis said. "But with multiple introductions comes an increased likelihood that one of the agents will become invasive as well. So, what we're trying to do is to figure out which one is the most likely to actually have an impact on garlic mustard and release as few agents as possible."

The computer model simulates how the populations of pest species vary in relation to introduction, growth cycle and environmental stressors. Scientists enter the biological control agents into the program one at a time until the perfect pest is identified. Scientists then collect data during field experiments and enter it into the computer model to make the most accurate predictions possible.

For garlic mustard, the computer identified a tiny weevil, Ceutorhynchus scrobicollis. This insect, which is no larger than an "o" in 12-point type, is a native pest to the plant in Europe; it feeds on the plant at several stages of its life cycle.

Scientists perform a stringent battery of tests in a quarantined environment before they release the control agent. In the case of garlic mustard, the weevil was exposed to no-choice feeding tests on 76 different species. Forty-five of these species were in the cabbage family, of which garlic mustard belongs. Test plants within the cabbage family included horticultural varieties. If the weevil liked, and could complete its life cycle on, cabbage, it could prove a threat to an important agricultural crop. This particular weevil passed that test and proved it was an acceptable biological control agent for use with a wide variety of plants.

The weevil is scheduled for release into an infested forest once it receives approval from the species evaluation and quarantine arm of the USDA, the Animal and Plant Health Inspection Service. Davis believes the simulation models provide the guidance to effectively and safely select biological control organisms to reduce the threat of invasive plants.

Garlic mustard came to the United States from Europe in the 1870s as a culinary herb. The weevil, its natural enemy, did not make the same journey.

CSREES funded this research project through the National Research Initiative Biology of Weedy and Invasive Species in Agroecosystems program. Through federal funding and leadership for research, education, and extension programs, CSREES focuses on investing in science and solving critical issues impacting people's daily lives and the nation's future. For more information, visit