Japanese Beetles Released in Maine to Devour Invasive Tree-Killing Insects

Japanese beetles, which are likewise regarded as non-native pests, will be used by authorities to combat the hemlock woolly adelgid, an invasive insect that has been damaging trees in Maine.

The Hemlock Woolly Adelgid

In an ongoing bug war to stop the spread of an invasive insect that has been destroying hemlock trees in Maine for the past 20 years, forestry officials have begun a promising move.

Since its introduction to southern Maine in 2003, the native to Asia hemlock woolly adelgid has been gradually moving along the coast as it moved inland. As recently as Acadia National Park, millions, if not billions, of the insect have been found, according to Colleen Teerling, a Maine Forest Service entomologist.

Non-Native Japanese Beetles: Sasajiscymnus Tsugae

"Biocontrol," or the use of a predatory insect, is one method for reducing the rate of spread of the woolly adelgid. Japanese beetles known as Sasajiscymnus tsugae, another Asian insect that consumes woolly adelgids but doesn't harm trees, have been cultivated in colonies by the state since 2004.

In the Woodward Point Preserve in Brunswick, Teerling, with the aid of the Maine Coast Heritage Trust, attached ten colonies with around 100 beetles each to ten trees that were home to woolly adelgids on Monday.

Teerling reported that, regrettably, they were able to find many trees with adelgid on them.

She claimed that because beetles can easily move from tree to tree, they are the most effective weapon against woolly adelgids in woods. The only commercial manufacturer of Sasajiscymnus tsugae beetles, Tree Savers, sold the insects to the Maine Coast Heritage Trust for roughly $2 each.

Invasive Insect in Maine

In the 1950s, Japanese adelgids were introduced to Virginia, where they subsequently moved north to Maine and south to Georgia. They spread quickly in the US and lack any natural predators. On hemlock, woolly adelgids lay up to 500 eggs in each of their two annual egg batches, which are produced exclusively by females.

Beachgoers in Kennebunk and Wells reported having black spots on their feet during the summer of 2021, which researchers later determined to be the result of dead woolly adelgids.

According to Teerling, the invasive species is migrating inland and eastward along the shore.

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Preventing The Spread of an Infestation

Teerling advised homeowners with infested hemlock trees to use horticultural oil as a pesticide because beetles would otherwise merely relocate. She emphasized the importance of prevention, saying that cutting back hemlock trees so they don't contact other trees or nearby items will probably prevent an infestation since woolly adelgids, which lack wings, won't be able to crawl on them.

A few thousand more beetles will be planted this year than were planted in state woods last year, according to Teerling, who works for the Department of Forestry. In Freeport, Waldoboro, Edgecomb, Portland, and South Berwick, beetles will shortly be planted by officials.

She gave local land trust organizations credit for taking the problem seriously and investing in beetles to impede the spread of the woolly adelgid. As the woolly adelgid has established itself in Maine, she said the biocontrol, along with pruning and herbicides, will be a continuing necessity to safeguard hemlock trees.