Scientist seeks hardier caterpillar to combat invasive Tree of Heaven

SALISBURY — A fast-spreading invasive tree could soon meet its match, according to Boston-based scientist Michael LaScaleia, who spoke at the Scoville Memorial Library Thursday, June 11, about efforts to breed a webworm capable of keeping the common tree in check. The event was sponsored by the Salisbury Association Land Trust.

A scientist with the Arnold Arboretum, LaScaleia focused his talk around the Tree of Heaven, a highly adaptable tree native to East Asia that was introduced to the United States as an ornamental tree in 1784.

“The Tree of Heaven is a big point of concern,” LaScaleia said, adding that it grows rapidly and is tolerant of a wide variety of conditions. It is also the preferred host of the invasive spotted lanternfly, a highly destructive species.

LaScaleia said in any plant’s native habitat, specialized herbivores often help keep the populations in balance by eating them.

“They don’t eliminate it but they keep it in check,” he said.

In the United States, however, the Tree of Heaven does not have a native specialist herbivore.

One possible solution might be to introduce “biocontrols,” introducing insects that feed specifically on the invasive plant. LaScaleia said this approach has been successful when a specialized beetle was used to suppress purple loose strife populations, although it took decades of testing.

This approach can also backfire, he said, citing the introduction of the Asian lady beetle to combat black pecan aphids, which had unintended consequences.

“They have completely taken over,” he said. “It’s the only ladybug you see anymore.”

Rather than importing another species from Asia, LaScaleia is studying how the Ailanthus webworm (Atteva aurea) might work if certain obstacles can be overcome. While already in the United States, they only exist in warmer climates including the Southeast. The problem, he said, is that the webworm migrates north but cannot survive prolonged temperatures below 55 degrees Fahrenheit.

One primary reason they don’t work is that even though the Atteva aurea migrates north to New England, it doesn't survive in temperatures below 55 degrees Fahrenheit.

But LaScaleia said he is trying to breed an Atteva aurea that can survive the winter.

“In theory, we can create a caterpillar that can do something about the Tree of Heaven,” he said, adding that, if successful, "controlling an invasive plant does not equal eliminating it.”

After the talk, LaScaleia and some of the audience made the short hike to the Land Trust’s Vincent Preserve for field work and continued conversation.