DARBY, Mont. -

The Forest Service is spraying mature pine trees with insecticide at Lake Como campgrounds on the Bitterroot National Forest, north of Darby. It's an effort to prevent Mountain Pine Beetles kills.

The service sprayed Carbaryl on these same trees two years ago, and they remain healthy. The chemical is almost 100% effective. But it wears off after a couple years.

About 1,200 trees at Como and 600 in other campgrounds are getting a second dose.

Spray crews aim their spray nozzles as high as they can, and brush all the way down till the trunk is soaked.

Lodgepole and Ponderosa pines are a mountain pine beetles favorite food.

Individual trees have already been selected and marked.

"These trees are 100 to 300 years old," said forester Corinne Anderson, "they're giant Ponderosa pines."

The beetles should be flying in a couple weeks, so the trees need to be sprayed before July 1.

If the beetles boar into a tree that's been treated, they will ingest the Carbaryl and die.

Workers move quickly. They hope to get all 1,200 trees sprayed in two days. It's a workout.

"It keeps the blood flowing and keeps the bugs off the trees," said sprayer Garret Smith.

The region's most popular recreation area is also a hot spot for pine beetles. Many trees on the ridge overlooking Lake Como have already been hit, and won't survive.

Carbaryl is a common insecticide used in forests, range ground, commercial agriculture and home gardens.

This spray project costs $25,000.

"In addition to the Carbaryl we use a pheromone patch too," said Forest Service planning officer Jerry Krueger. It tells the beetle to go away, there's no vacancy in this tree.

There's a third approach to managing the rec area. The Forest Service is thinning trees too.

"If you walk down the middle of this forest it's just majestic," said Anderson.

But critics said chemical sprays are never healthy, and pine beetles are ancient Montana natives just doing a job.

Silviculturist Jerry Krueger said that is true. "They're part of the natural function of the forest ecology," he said.

The beetles are cyclical. They may be at their peak in the Bitterroot. "Which is why we're trying to be very diligent in taking care of these special places like Lake Como," said Krueger.

Over the next two years, the Forest Service will monitor these trees to see how well they weather the beetle infestation.