Like Burma Shave advertisements, a series of signs along the Pennsylvania Turnpike once read: “You can go, A mile a minute, But there is, No future in it.”
At the University of Delaware, entomologist Judy Hough-Goldstein is working to slow down a different speeder: mile-a-minute weed.
Although this prickly vine with triangular leaves and iridescent blue berries doesn’t grow as fast as its name implies, it can branch out a good 20 feet a season in the Mid-Atlantic region, the professor of entomology says. And the weed is rapidly invading new territory.
Since arriving in the 1930s at a nursery in Stewartstown, Pa., mixed in with holly seeds from Japan, mile-a-minute weed has spread to 10 states and the District of Columbia.
Also known as “Asiatic tear-thumb” due to its sharp spines, this weed plagues forests and meadows, parks, orchards, roadsides and rights of way, climbing over everything in its path. Seedlings, shrubs and trees are completely enshrouded, rising up like topiary stalagmites from a field of green. The weed blocks sunlight from reaching the vegetation, weakening and in some cases killing it.
However, a natural nemesis — the Asiatic weevil Rhinoncomimus latipes — is now coming on the scene, after extensive testing by Hough-Goldstein and her students. The weevils were introduced in Delaware in 2004 as part of a biological control program.
The research began in 1999 when the U.S. Department of Agriculture (USDA) Forest Service contacted Hough-Goldstein to see if she would be interested in doing the tests to determine if the Asiatic weevil is host-specific to mile-a-minute weed in the United States, just as it is in China. She became the first researcher in the world to test and obtain a permit to release the weevil as a control agent for the weed. Today, her lab is still the only one in the United States — and one of only a handful in the world — attempting to control the invasive plant through biological means.
She notes that Ding Jianqing, a collaborator at Wuhan Botanical Gardens in China, has been critical to the study, as well as the USDA Beneficial Insect Research Laboratory and its quarantine facilities near her lab at the College of Agriculture and Natural Resources.
“If the weevil switches hosts, it’s likely to be a close relative. So our mission was to expose the weevil to various plants over several weeks and see what happened,” she says.
Although some insects are generalists that feed on multiple species of plants, most insects are specialists, linked by evolution to only one or two host species.
“Plants can produce hundreds of toxic chemicals, so the insects that depend on these plants need to be very in tune with them to be able to thrive,” she says.
A telling clue is where an insect lays its eggs. The researchers found that these weevils, only as large as half a grain of rice, lay eggs on mile-a-minute weed, but not on other plants. The larval stage of the weevils feed inside the stems, while the adults bore holes in the leaves.
Although the weevil will never eradicate mile-a-minute weed, the long-snouted insect can definitely curb it. At a test site on Pea Patch Island in Delaware Bay, location of a Civil War prison and one of the East Coast’s largest heron rookeries, the weevil has reduced the infestation by half in only two years.
Yet other members of the ecosystem are aiding the weed’s spread. Deer and birds eat the tart berries and disperse the seeds.
Resource managers in Massachusetts contacted Hough-Goldstein about using the weevil to put the brakes on a growing infestation in an area with rare and endangered plants.
Although scientific models have shown that the Asiatic weevil will have naturally expanded its range to New England in 30 years, resource managers there won’t have to wait that long. The New Jersey Department of Agriculture is rearing the weevils and recently sent some to Massachusetts for the first time.
The unsung heroes in the research are her graduate students, Hough-Goldstein says. Over the past decade, they’ve grown hundreds of plants in the greenhouse and insects in the lab, conducted multiple tests in the lab and field, documented the extent of the weevils’ stem boring and defoliation, and helped to report the results to scientists and the public.
“This work is really a credit to them,” she says of the high-stakes effort.
“Mile-a-minute weed could infest a high percentage of the United States and Canada,” she notes. “Although this is not a silver bullet, the signs are positive that this weevil will help put infested areas back into ecological balance.”