CONCORD, N.H. — New Hampshire forestry officials plan to remove about 120 acres of red pine trees from a state park this winter to slow the spread of an aggressive insect that’s destroyed thousands of the trees in southern New England.

The nearly microscopic brown insect is called red pine scale and was detected at Bear Brook State Park in Allenstown in August.

It’s the first documented case of the insect in New Hampshire, though the bug’s been a longtime headache in Connecticut, Rhode Island and Massachusetts, which have been losing the trees for years. Parts of New York, New Jersey and Pennsylvania also have battled red pine scale.

“We’re just going to try to cut it all out and hope that it doesn’t spread,” said Kyle Lombard, forest health program coordinator for New Hampshire’s Division of Forests and Lands.

“There is no red pine left in Connecticut, and they’re cutting as fast as they can in states like Rhode Island and New Jersey. They’re just getting it out of there. It’s all dying.”

In the past, he said, Connecticut tried to introduce insect predators that would feed on the red pine scale, and experimented with pesticides, but nothing really worked.

Ken Gooch, forest health program director for Massachusetts, said on average, his state loses 300 to 500 acres of red pines a year.

Most of the loss has been in western Massachusetts, around the Quabbin Reservoir. He said some red pines also have died because of a common tree disease.

“The only thing that we tried maybe 15 years ago was trying to cut it out as soon as we found it, but that didn’t stop it,” Gooch said.

“It’s just like hemlocks’ wooly adelgid,” a tiny beetle that has attacked hemlock trees in the region. “The birds spread it,” Gooch said. “You can’t stop that.”

While there are some native red pine stands in central and northern New Hampshire, Maine and Vermont, the tree is not considered native to the region; it is native to the upper Great Lakes through southern Canada west to Manitoba, and on mountainous ridges as far east as West Virginia.

Many of the trees in New England and elsewhere were planted in the 1930s by the Civilian Conservation Corps, the work-force program under President Franklin D. Roosevelt, to restore forests.

The trees grew fast and withstood cold weather.

No one’s quite sure where the insect originated.

Forestry officials say it was first reported in Connecticut in 1946.

They think it was most likely introduced to the United States on exotic pines planted at the New York World’s Fair in 1939.

Red pine scale is easily spread by wind, birds and squirrels.

The first visible signs of infestation include bright “flagging,” or discoloration of the lower branches, followed by the swift decline of the entire crown.

A tree can be destroyed within a few years.

Visitors to Bear Brook State Park will eventually notice the missing trees, many of which are at the park’s entrance, said Will Guinn, regional forester for New Hampshire’s Forest Management Bureau.

But the landscape won’t be completely barren; there are nearby stands of white pines at the park that are waist-high to 10 feet tall.

“That will be the next generation of forest coming along,” he said.

The goal is to get the affected trees removed while they are still alive in time for a commercial timber harvest, Guinn said.

“If we wait until the trees are dead, we’re going to have to pay to have thousands of trees removed,” he said.

Guinn said red pine scale has not been detected in any other New Hampshire parks.

Lombard said the insect doesn’t have the ability to withstand very cold winters, which is why he thinks the red pines in northern New Hampshire won’t be affected.

“But we said that about southern New Hampshire for the last 30 years,” Lombard said.

“So it crept finally into southern New Hampshire. So I would expect in 20 to 30 years maybe it would creep into northern New Hampshire. I don’t know; it depends what winter temperatures do.”