Voluntown — Hikers and swimmers visiting the Green Falls Pond area of Pachaug State Forest this summer probably won’t notice some of the newest wildlife to occupy the area.

Nonetheless, they’ll have reason to be grateful to the tiny creatures if they enjoy the towering hemlocks there.

Last week, an entomologist from the Connecticut Agricultural Experiment Station joined foresters from the state Department of Energy and Environmental Protection in releasing 300 Japanese beetles called Sasajiscymnus tsugae on three hemlocks near the Green Falls River that were showing early signs of infestation by the hemlock woolly adelgid.

The pests "cause damage by depleting the hemlock’s starch reserves, which in turn reduces the tree’s ability to grow and produce new shoots," according to a USDA informational publication.

The tiny black beetles, less than one-eighth of an inch long, eat the adelgids and pose no threats to other species, said Carole Cheah, research entomologist at the agricultural experiment station’s laboratory in Windsor.

“These are still healthy trees,” she said. “It was an emerging infestation. The beetles should multiply rapidly.”

Hemlock woolly adelgids, an invasive pest from Japan, first began infesting hemlocks in Connecticut in 1985, and caused the collapse of hemlock stands statewide, including areas in Old Lyme and at the Connecticut College Arboretum in New London. In 1995, a federal permit was granted for the release of the Japanese beetles as a biological control on the adelgids.

From 1995 through 2007, more than 176,000 beetles were released at 26 sites around the state. Over the past few years, the adelgid infestation appears to have subsided, thanks to the effects of the beetles and some severe winter weather in recent years, bringing the adelgid levels to the lowest point since 1995, Cheah said.

But the drought of the last two years has left some hemlock stands stressed and susceptible to new infestation, she said. When DEEP foresters alerted her to early signs of a new infestation in a grove of hemlocks in Pachaug State Forest, she saw it as a unique opportunity to head off a widespread outbreak.

She contacted Tree-Savers, a Greentown, Pa., company that raises the beetles. The company offered her 300 beetles free of charge, so Cheah drove to Pennsylvania to pick them up. They can cost as much as $2 per beetle, she said.

“It was very generous of them,” she said.

To release the beetles, Cheah placed the insects on cut hemlock branches that were bundled and tied onto the trees in the forest. She plans to return to the site to monitor the effectiveness of the release.

She advised land trusts and private forest owners interested in releasing beetles on their property to contact Tree-Savers at tree-savers.com.

j.benson@theday.com