Insects being deployed in war against invasive species

            After wandering through the forest at Cromwell Meadows Wildlife Management Area, Claire Rutledge selects a dying ash tree and goes to work. She pulls out her drawknife – a foot-long sturdy blade with handles on either end – and slams it into the tree at chest height, then draws it downward until the bark can be easily peeled from the tree in long vertical strips.

            As she does so, she searches for evidence of emerald ash borers, an invasive beetle from Asia that is expected to kill all of the ash trees in the Northeast in the coming decade. After peeling away several strips of bark, she reveals a series of winding tunnels like

Claire Rutledge peels bark at Cromwell Meadows (Arnold Gold)

switchbacks on a hiking trail that were created by the beetle’s larva as it consumed the tissue between the tree’s bark and wood. She also points out several holes in the bark created by adult beetles as they emerged from the tree to find a mate.

            But Rutledge, an entomologist with the Connecticut Agricultural Experiment Station in New Haven, and her team of seven colleagues aren’t just seeking evidence of the beetle. They’re also looking for tiny parasitic wasps, offspring of a species Rutledge had released several years earlier to kill the beetles. It’s a strategy called biological control, whereby the natural predators of the beetle in its native range in the Far East are released locally in an effort to keep the beetle in check.

            The emerald ash borer was first discovered in the United States in 2002 near Detroit, and it slowly expanded into ash forests in nearby states. It was found in New York in 2008 and Connecticut and Massachusetts in 2012, though it probably arrived a few years earlier. Although its rampage through the region isn’t expected to end before every mature ash tree is dead, scientists like Rutledge hope that efforts to control the insect by releasing the parasitic wasps will allow future generations of the trees to fend off the invader.

            The wasps use their long stinger-like ovipositor to lay their eggs through the bark and into the beetle larvae. When the wasp larvae hatch, they kill the beetle larva by eating it from the inside out.

            “For a little while, the beetle larva keeps eating the tree and looks fine, but eventually it stops looking so fine and looks like a bag of Cheetos with a bunch of wasp larvae in it,” says Rutledge, who has released at least one of three species of parasitic wasps at 14 sites around the state, beginning in 2013.

            She measures the success of her efforts by whether the wasps are sustaining themselves in the environment and by collecting and dissecting emerald ash borer larvae to determine how many have been parasitized by the wasps. “We’re recovering the wasps all over the place, so they seem to be doing pretty well,” she says. “And 20 to 40 percent of the beetle larvae we find are killed. So we consider it a success.”

             Non-native insects and plants have been invading the United States for more than a century, costing billions of dollars and causing significant ecological harm. Removing these invaders by conventional means – the application of chemical pesticides and herbicides or manual removal of plants – is a labor-intensive exercise that seldom works for long. And although biological control does not completely eliminate the problem either, practitioners say it is a self-sustaining strategy that is cost-effective and causes less harm to...

Read the rest of the story in the May 2020 issue of Connecticut Magazine.