What happens if the control agent also becomes an invasive species?
A stringent battery of tests is performed on each biocontrol agent in quarantine before it is ever released. For example, garlic mustard is in the same family (Brassicaceae) as cabbage, so one test might be to only feed the weevil cabbage and see if it survives on it or can reproduce on it. If it does, then the possibility exists that it could move from the garlic mustard and threaten cabbage plants, which we dont want to happen. But, this particular weevil has passed that test for a wide variety of plants.
Davis said that there are different strategies for biological control. One strategy is inundative in which the control agent eats its way through the garlic mustard and then dies out itself because there isnt anything left to support it. The other strategy is to introduce a natural enemy that will just bring the population down to a lower level and the plants and pests just continue to coexist. The idea is that you reunite plants with a natural enemy from back home which in garlic mustards case is Europe. In Switzerland garlic mustard and the weevil coexist and neither one is invasive.
Garlic mustard was brought to the United States from Europe innocently in the 1870s as a culinary herb but its natural enemy didnt accompany it.
Davis says there are some concerns among ecologists about biological control because of the risk of negative effects on nontarget species. But when you have invasive plant species covering very large acreages its almost impossible to manage by hand, he said. There are herbicides that will work on garlic mustard, but it infests millions of acres of forest and theres no way you can get out there and spray all of that. And because garlic mustard has a really long-lived seed bank, in order to eradicate it, youd have to hit it for about eight to ten years in a row.
Pending approval from APHIS-PPQ (th
|Contact: Debra Levey Larson|
University of Illinois at Urbana-Champaign