Alarmed scientists first discovered the beetles last year along a front stretching more than 200 miles, from central Long Island to Cape Cod and Martha’s Vineyard, a region long thought to be far too frigid for these tiny beetles, barely different in size and color from a chocolate sprinkle.

“When I heard they caught a live beetle in Massachusetts,” Dr. Rutledge said, “that really freaked me out.”

Now that the beetles are in New England, they are probably there to stay, state and environmental officials said. And if there is a severe outbreak, the region could lose much of its pitch pine forests. Many of the forests are already unhealthy, a result of overcrowding, making them especially susceptible to the pine beetle’s attacks — boring through bark, laying eggs and spreading a crippling fungus — and many state forestry divisions do not have the resources to combat them.

Scientists are concerned that the beetles could destroy the remaining tracts of the pitch pine forest, an ecosystem that once carpeted the Eastern Seaboard but now exists mostly in pockets — the Cape Cod National Seashore, the Albany Pine Bush Preserve and smaller forests — and is home to more than a dozen endangered species, such as the tiger beetle and several types of butterflies.

“I don’t think people have a strong understanding of how at risk these forests are,” said Kevin J. Dodds, a scientist who runs the southern pine beetle response in the Northeast for the United States Forest Service.