Putting the Brakes on Mile-a-Minute Weed

UD Scientists First Release Asian Weevil as Biocontrol

How do you combat a plant so invasive that it is overtaking native plants in natural areas throughout the northeastern United States? With a weapon the size of half a grain of rice-the Asian weevil, a form of beetle.

A David and Goliath scenario? That's the strategy. The U.S. Department of Agriculture Forest Service counting on the weevil's voracious appetite for mile-a-minute weed, which is native to China, to disrupt the invasive weed's onslaught, thus protecting native vegetation.

Six years ago Dr. Richard Reardon of the USDA Forest Service invited University of Delaware entomologist Judith Hough-Goldstein to take part in a bio-control project targeting a highly invasive plant - Polygonum perfoliatum -introduced accidentally into a Pennsylvania nursery in the 1930s. Mile-a-minute weed has been on the march ever since, depriving indigenous plants of sunlight and often out-competing natives in spring seeding.

"This project really interested me," says Hough-Goldstein. "The weed is a serious problem in our area. It has a stranglehold on White Clay Creek State Park, a much-visited recreational site in Newark, which shows how close to home the problem is."

For several years Hough-Goldstein and her graduate students researched possible bio-controllers. A biological control is an alternative to traditional chemical methods for control, in this case, an herbicide. But herbicides are not practical in areas of dense plant populations because the practice would negatively affect the ecosystem.

Out of all the bio-controls they considered, the scientists decided the Asian weevil, Rhinoncomimus latipes , seemed to offer the best solution. Their in-laboratory research established that the Asian weevil can control the mile-a-minute yet do no harm to native plants. A real-world study was needed, but introducing non-native species of any kind can be done only with the expressed permission of the U.S. Department of Agriculture. The federal agency must be certain that any biological control agent introduction into the wild is host-specific and poses no threat to the environmental.

After five years of study and documentation, approval for the trial Asian weevils release came in the middle of summer. For the first time on July 21, Hough-Goldstein's graduate assistant Eric Reynolds and Reardon released 200 insects into an area of White Clay Creek State Park outside of Newark where mile-a-minute is especially prevalent. The site will be monitored closely for results, but science has its own time. The impact the weevils have on mile-a-minute weed may take a long time to become noticeable.

"It could be anywhere from five to 10 years before measurable control becomes obvious at White Clay Creek," says Hough-Goldstein. "Only a few hundred weevils were released, and it will take time to determine if they can effectively control the weed."

"We're not even positive the weevils will reproduce and/or survive the winter," adds Reynolds. "Just releasing laboratory-reared weevils into the wild is not enough. The insects must be able to adapt, reproduce and survive themselves-just as their mile-a-minute target has-for real impact to be made."

Efforts are being made to speed up the control process, however. Following the official release in White Clay Creek Park, a number of Asian weevils were transported to the Phillip Alampi Beneficial Insect Rearing Laboratory in Trenton, N. J., where researchers hope to find a way to rear the weevil quickly -the greater number available for release, the faster results will be seen.

"We are realistic. The weevils won't eliminate mile-a-minute," says Reardon. "The strategy is that their feeding will slow the weed's aggressive spread."