ANNAPOLIS – Scientists hope to get rid of an invasive vine that was accidentally introduced from Asia decades ago by unleashing a vine-eating bug — also from Asia.
Releasing a foreign species to control a nonnative plant may seem like throwing oil on the fire, but with enough caution it can be best way to put the brakes on a seemingly unstoppable invader, said Maryland Department of Agriculture entomologist Bob Trumbule.
Trumbule released hundreds of Asian weevils in a Howard County park this summer to test their effectiveness against mile-a-minute weed, a thorny vine that has spread across the Mid-Atlantic. The July release follows similar trials last year by the U.S. Fish and Wildlife Service on a Susquehanna River island in Maryland.
Mile-a-minute weed can grow 40 feet in a year, forming masses that drape over native and landscape plants and can eventually kill them by blocking out sunlight. It “is almost a poster child as to why we should be concerned about invasive species,” said John Peter Thompson of the National Invasive Species Council Advisory Committee.
The Chinese weevils, Rhinoncomimus latipes, were selected after researchers in Asia fed 49 different species of plants to a variety of insects to find one that could not live without mile-a-minute weed. The weevil was the only one to make the cut.
In 1999 it was sent to the United States, where University of Delaware entomologist Judith Hough-Goldstein test-fed it another 28 species of plants.
“We were really lucky with this weevil,” Hough-Goldstein said. “It is practically indestructible.”
Even more importantly, the weevil needs mile-a-minute to survive. Biologists hope they will chew enough leaves and bore into enough stems to reduce seed production and ultimately control the spread of the vine.
Introduction to test sites around the Mid-Atlantic began in 2004.
“There’s a long history of biological control in this country and much of it has not worked,” said Kerrie Kyde, an invasive plant specialist with the Maryland Department of Natural Resources. But rigorous testing in recent years has given her hope.
“I am willing to go out on a limb and say that Rhinoncomimus will do a really good job at reducing mile-a-minute populations,” she said.
The 2-millimeter-long insects resemble coarsely ground black pepper at first, but a closer look at their long snouts and round bodies reveals an anteater-like creature, Trumbule said.
He returns once a month to Meadowbrook Park in Ellicott City, where he released 500 weevils in July, and records what affect they are having on the weeds, a routine he will continue until the first frost kills the vines.
Climbing down into the small stream valley, Trumbule checks 10 sites along a 100-meter line. At each site, Trumbule sneaks up slowly, careful not to touch the plants. The slightest disturbance causes the tiny insects to drop off, where they will not be found.
Besides measuring the weed coverage at each site, he counts weevils and their evidence, small round holes in the leaves and damage to plant stems from burrowing larvae.
Trumbule then repeats the process in a control plot where weevils have not been released.
Results have been promising, but not conclusive, Trumbule said. The weevils are reproducing. With a life cycle of less than a month, the lone weevil Trumbule found this month could be the grandchild of one of those released in July.
The Howard County trial follows weevil releases in 2006 and 2007 on Garrett Island at the mouth of the Susquehanna by Rachel Cliche, an invasive species specialist with the U.S. Fish and Wildlife Service. Cliche has seen reproduction and over wintering of her weevils from one year to the next.
Within a few years, she hopes to also test at Eastern Neck Wildlife Refuge in Kent County.
A New Jersey test with thousands of weevils eradicated all the mile-a-minute weed. But then the bugs died off because they had nothing to eat. The weeds came back the next season.
Biologists note that conditions are different in Maryland and that this year has not been ideal for studying weevil activity because of the drought, which has even withered the normally robust mile-a-minute weed.
The weed’s haters acknowledge that it will take years to know whether the weevil will work. And they know the bug has its work cut out for it.
“I’ve seen the damage,” Cliche said. “Once they multiply I think they are going to do a number on it. But it’s a long shot that they would get rid of mile-a-minute weed.”