Invasive plant meets its match when weevils come calling

They look like poppy seeds with legs as they tumble out of two pint containers and onto the leaves of a scraggly vine sunning itself near a pine tree.

But looks deceive. In a split second, the 500 bugs attack the plant like vegan conventioneers at an all-you-can-eat salad bar, chewing the leaves and burrowing into the stems.

These are some of the smallest state employees — weevils, actually — doing work usually carried out by chemicals and earth-moving equipment. Their meal is an invasive Asian plant that arrived in York County, Pa., in the mid-1930s and has spread since to 12 East Coast states.

The plant, called mile-a-minute weed, moves a little slower than that, but not much, strangling trees and native plants in its path. It grows as much as 6 inches a day and it is prolific: a single plant can produce 2,000 seeds that can be spread by birds, animal fur and water.

That suits the weevils, Rhinocominus latipes, just fine. Mile-a-minute is all they eat.

The State Highway Administration released weevils this summer at seven wetlands, including one in Jessup. Four more sites — one in Baltimore County near Oregon Ridge — are on the schedule. The state is spending $25,000 on the bug program this year.

On a recent tropical morning, Bob Trumbule carried a soft-sided blue cooler into the woods, past some small patches of mile-a-minute as he sought the mother lode. Inside the cooler, the weevils awaited the dinner bell.

"I see something that looks suspicious," said Trumbule, an entomologist with the Maryland Department of Agriculture, as he crossed a clearing to a large thicket of the vines where a few Japanese beetles munched away.

While the Japanese beetles do more immediate damage to mile-a-minute by devouring entire leaves, the weevils lay waste to the whole plant over time, Trumbule explained. The weevil eggs produce larvae that burrow into stems to kill the plant and prevent the release of its seeds.

As far as the state is concerned, mile-a-minute has no redeeming qualities. It can take over vast tracts, especially where the soil has been disturbed for highway construction. Trees and ground covers planted by the state after a project can be overcome as the weed blocks the sunlight.

"If this is left to grow unchecked, it will grow 15 feet up into the trees," said William Klingelhofer, a highway administration environmental analyst.

Yet the plan is not to eradicate the weed. The state wants to leave just enough to keep the weevil population healthy, Trumbule said, "bringing everything back into balance."

Federal scientists began looking for host-specific insects to prey on mile-a-minute more than two decades ago. The weevils, imported from Asia, got their first test under controlled conditions in Delaware, and the government approved their use in July 2004. Weevils have been released in 10 states since then.

Howard County put them to work at Meadowbrook Park near Columbia in 2007; three years later, the highway administration released 1,000 weevils in West Friendship at Interstate 70 and Route 32.

State officials were so impressed that they began raising weevils at the agriculture department headquarters in Annapolis last year using a method developed by their counterparts in New Jersey. Development from egg to adult takes about 28 days, and during that time, weevils can be quite demanding.

"When they get going, you run out of food and you have to release them or they'll eat you out of house and home," said Mary Jo Klovensky, the agriculture inspector who is head weevil wrangler and packs them for travel to their new homes.

But their appetite is exactly what the state wants. During the Mid-Atlantic growing season, the weevils go through at least four overlapping generations, which ensures heavy pressure on mile-a-minute. Their range is about six miles. In winter, the adults bed down in the soil or leaf cover.

The proof of the program's success comes when state officials get calls from residents about an outbreak of mile-a-minute.

"By the time we get there, the weevils are already there," Trumbule said. "They're moving pretty fast."

Copyright © 2018, The Baltimore Sun, a Baltimore Sun Media Group publication | Place an Ad