Students and Retirees Bond Over Weevils and Weeds


July 28, 2009

Releasing Weevils
Jane Krick and Ellen Lake release weevils into a patch of mile-a-minute weeds that threaten native plantings at Kendal-Crosslands retirement home. (Paulding Phelps)
The Kendal-Crosslands retirement community (KCC) in Pennsylvania is host to more than book clubs and bridge groups. Residents can often find students from nearby University of Delaware (UD) scrambling through KCC’s fairly substantial patch of mile-a-minute weeds (Persicaria perfoliata), trying to eradicate the invasive, prickly and sun-hoarding annual Asian vine that grows 20 feet or more after sprouting in the spring until the first killing frost in the fall.

The battles against the mile-a-minute weed and other noxious weeds across the United States cause about $128 billion in damages and losses to the country’s economy annually. And invasive weeds aren’t just expensive: They can alter ecosystems by removing valuable nutrients from the subsoil, altering water flows and out-competing native plants for sunlight. Recent studies are also showing that the effects of climate change on the environment may foster the spread and frequency of the destructive plants.

UD students are hoping they have found a solution for this particular plant. The students are using KCC as one of their test sites for biological controls on the mile-a-minute weed. The group, spearheaded by UD Ph.D. student Ellen C. Lake, began experimenting last year with combating the invasive weed with a very specific Chinese mile-a-minute weevil, pre-emergent herbicides and native plants. And residents at KCC are happy for the help.

“We’ve got that invasive [plant] here and it’s a real darn nuisance,” says Ted Brinton, a resident at KCC and chair of the Crosslands Nature Conservancy, the community committee that oversees environmental projects. “It’s well-named. You can stand there and almost watch it grow.”

KCC is situated on 500-plus acres of land, part of which is designated open space, and it is on this open space that the mile-a-minute weeds dominate many native plants. “A number of us who are residents here saw the need for conservation work of various sorts,” explains Brinton. “It was pretty obvious, so we split up responsibilities for managing trails, cutting invasive vines and managing meadows and woodlands.”

“It’s a very well-educated, engaged community,” says Lake. “Most of the time when we’re out in the field working, residents will stop by and ask how everything is going.” In late June this year, KCC residents offered Lake and her assistants a helping hand with the release of several hundred weevils onto their grounds in hopes of slowing the spread of the community’s mile-a-minute weeds.

According to Brinton, the average age at KCC is in the low eighties, which means most of the residents were about ten years old when the mile-a-minute weed really first took hold in the United States. In 1938, a nursery owner in York County, Pennsylvania, imported holly seeds from Japan. He planted the seeds and a bizarre vine emerged. It had bright blue iridescent berries and looked different from anything he had ever seen. The nursery owner thought the vines might have some horticultural value to them so he continued to let the vines grow. The nursery was then abandoned a few years later.

Rhinoncomimus latipes is the biological control weevil for mile-a-mintue weed, and cannot reproduce on any other plants. (Ellen C. Lake, University of Delaware)
In 1948, botanist E.T. Moul wrote an article in Rhodora: Journal of the New England Botanical Club that this strange vine had spread from the abandoned nursery to several adjacent farms and should be eradicated before it had the chance to spread further.

“Of course, nothing was done,” explains Lake, “so now the mile-a-minute weed can be found north into Connecticut and Massachusetts, south into Virginia and West Virginia, and west into Ohio. And it’s still spreading.” According to the Plant Conservation Alliance, the mile-a-minute weed’s current distribution only covers about 20 percent of its likely potential range. Moreover, a single mile-a-minute plant can produce more than 2,000 seeds in a season.

“You can definitely say this plant seeds prolifically,” says Lake, “[so] you need to look at treating mile-a-minute weeds year after year to keep it out of an area, and that’s one of the advantages of biological control. The insects are self-perpetuating, so they’ll remain in an area as long as there are mile-a-minute weeds to feed on.”

In 1996, a biological control program specifically targeting mile-a-minute weeds was launched by the U.S. Forest Service, during which 111 different insect species were tested for their abilities to combat the invasive plant. Eventually, a 2-millimeter long, stem-boring Chinese weevil was selected from the group because it was found to be the most host-specific to the mile-a-minute weed. The weevil could not reproduce on anything other than mile-a-minute vines.

Control Weevils
Rhinoncomimus latipes is the biological control weevil for mile-a-mintue weed, and cannot reproduce on any other plants. (Ellen C. Lake, University of Delaware)
In 2004, a permit was made available for the release of the mile-a-minute weevil in the United States and the University of Delaware was one of the original recipients. “Adult weevils lay eggs on the leaves of the mile-a-minute weeds,” explains Lake. “The eggs will hatch after a few days and the larvae immediately bore into the stem and eat inside the plant. The larvae will feed for seven to ten days before dropping or crawling into the soil, and they’ll pupate there for a few days before they emerge as adults and begin feeding on the plant’s leaves. So we really get two-pronged damage, adults feeding on the leaves and the larvae feeding internally.”

Since the project is still in its infancy, it may take some years of research before Lake will know how many weevils it will take to establish a self-sustaining colony, how effective the weevils will be in reducing the spread of mile-a-minute vines, or how effective the weevils are in comparison with applying herbicides to the vines or shading the vines with competing plants and trees.

“In the long-term goal of biological control, you’re never going to completely eradicate the problem weed,” says Lake, “but eventually you reach equilibrium between the insect and the invasive plant. And the ultimate goal of this project is to no longer have the mile-a-minute weed be the dominant plant in those areas and restore the native plants that should be there.”

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Published: July 28, 2009