|Colleen Teerling held a netted captive wasp, which prey on predator of emerald ash borer beetles. (Fred Field for The Boston Globe)|
Novel system keeps lookout for pesky pest
SANFORD, Maine - Measuring less than an inch long and flaunting a shimmery green shell, the emerald ash borer beetle resembles the precious stone of its namesake. But in North America, the insect is anything but prized.
Emerald ash borer larvae have killed tens of millions of ash trees in the United States since the beetles arrived in Michigan in 2002, probably in a wood shipment from Asia, and they have now infested areas as far south as Virginia and as far north as Canada.
Stopping the invasive species is challenging because the first sign of the beetle is often when trees start dying. By then the bug has usually spread widely. The larvae, which live under the bark, aren’t always killed by insecticides.
Now Maine, which borders already-infested Quebec, has devised a novel early warning system, combining the maternal instincts of wasps with the tenacity of net-wielding volunteers in communities across the state. The wasps catch beetles to nourish their young, and the volunteers - from selectmen to Girl Scouts - catch the wasps.
It is the first large-scale effort in the United States to use a native species to monitor an invasive one, said Colleen Teerling, entomologist for the state Forest Service.
“It’s a strange concept, but it seems to be working,’’ said Teerling. “We want to be able to find this thing as soon as possible. It’s crucial.’’
Hundreds of beetles have been collected at 11 locations around Maine, with no sign of the emerald ash borer.
On hot summer days, the nickel-size wasp, known to entomologists as the Cerceris fumipennis, goes hunting, and the metallic wood-boring beetle is one of its prime targets. New England is home to other metallic beetles - which sparkle in gold, silver, blue, and other colors - but trees recognize and have developed a defense against these native insects, releasing debilitating hormones into their bark, which prevent the larvae from turning into adults.
Once a female wasp finds its prey, it paralyzes the beetle with its stinger and carries it back to its burrow, which is usually dug in a dry sandy area like a baseball field. There, the wasp lays an egg on the bug, so that when it hatches, its offspring will have a living meal to feast on.
“It’s really amazing,’’ said Philip Careless, an entomologist with the Canadian Food Inspection Agency, whose research on using the wasp for “biosurveillance’’ gave Teerling the idea for the Maine project. “It’s like a sci-fi movie on a baseball diamond.’’
In his research, Careless showed that the wasps, which he likens to drug-sniffing police dogs, wouldn’t change their behavior once humans started taking their hard-earned kill.
“We wanted to make sure they wouldn’t abandon their nests because we’re stealing their baby food,’’ said Careless, who began his research while studying at the University of Guelph in Ontario. “If someone stole your groceries every time you got to your front door, you’d move to a different neighborhood.’’
Luckily, the mother wasp has tunnel vision when it comes to feeding her offspring. Once a beetle is taken away, she immediately hunts for more prey, and thus becomes a tireless, if unwitting, worker for the cause, said Careless.
On a sandlot at Emerson School in Sanford one recent afternoon, John Sherman and his wife and two children endured sweltering heat to chase down about 15 wasps.
“I got another one!’’ yelled John, Sherman’s son, before carefully taking the wasp out of the net, plucking away her kill, and placing it in a plastic bag.
The mother wasps are fairly easy to catch because they buzz around their burrows, which the volunteers mark with brightly colored pegs. Plus, they don’t sting, said Teerling.
The volunteers have been trained to identify the emerald ash borer and alert Teerling immediately if they catch one. Unless one is spotted, the day’s catch is stored in the volunteers’ freezers and mailed to Teerling at the end of the summer.
Over the summer, Sherman and his family collected 50 beetles, the goal that Teerling set for each of the 11 wasp colonies throughout the state. Sherman was relieved that no emerald ash borers were among their catch.
“This could be the next Dutch elm disease. You go down Elm Street in cities now, and you don’t even know why the street is called ‘Elm’ - all the trees are gone,’’ said Sherman. Like elm trees, which were ravaged by fungal Dutch elm disease in the 1960s and 1970s, ash trees are a popular choice for planting in cities and new developments. They are common in Maine because they can survive the salt spread on roads in winter and extreme temperatures.
Teerling said that training volunteers was easy and inexpensive, and she expects many more to sign up for next summer’s collections.
The Maine Department of Conservation has recommended that firewood from other states not cross the border into Maine. Wood chips and lawn mulch, which can come from anywhere in the United States, should be carefully inspected for the beetle, and if it is found, consumers should call the Maine Forest Service immediately, Teerling said.
Massachusetts is taking a lower-key approach than Maine, educating horticulturists, city arborists, and others about the emerald ash borer through a website devoted to invasive pests.
But in some other states, Careless is working with the US Department of Agriculture and the US Forest Service to develop “mobile colonies’’ of the wasps to monitor for the beetle in areas where there are no native colonies. He has tested the colonies (with tubes filled with sand where the mother burrows, kept in the back of his car) in infested parts of Ontario, Maryland, and West Virginia.
So far, the colonies work: the wasps bring back more beetles than are trapped by the sticky purple fly paper currently used by the USDA.
But Careless said the wasp strategy is unlikely to be widely adopted unless he finds a less labor-intensive way to use them. “Wasps are a sensitive biomonitoring tool,’’ he said, “but they are also a time-consuming one.’’