CHEYENNE (AP) - Spruce trees around town have been succumbing to bark beetles in alarming numbers, prompting the city to ask homeowners to help control the insects.

Recent mailings by the city ask residents to keep an eye on sick trees and, if those trees reach the point of no return, to cut them down and carefully dispose of the wood.

Lately bark beetles have made headlines for killing large numbers of trees in forests across the West. Several years of drought have been weakening trees, and several warmer-than-normal winters have been allowing bark beetles to survive from year to year.

The Cheyenne outbreak shows that urban trees aren't immune.

Half of the 1,200 trees in Olivet Cemetery are spruce, and 10 of those were removed in July due to beetle infestation. Another 12 trees are expected to follow soon, according to Randy Overstreet, assistant director of Cheyenne Urban Forestry.

Crews sprayed several cemetery trees Monday and Tuesday and planned to cover the rest of the cemetery soon.

Overstreet estimated that another 100 or so spruce trees around town - 10 percent of the city's total - are also infested. "It's not a high number," he said. "But it could be very high next year."

The beetles burrow under bark and lay their eggs. When the eggs hatch, the larvae feed on the tissue between the bark and the wood where most of the tree's nutrients are transported.

When the beetles consume enough of the tissue, the tree dies. They then exit through small round holes in the bark.

Overstreet said the tops of trees are the first part to turn brown, but the discoloration soon progresses downward, sometimes in a matter of days or weeks. Beetle outbreaks are tricky to manage, however, because symptoms are difficult to detect until it's nearly too late.

"The beetle could be in the tree and you would never know it," Overstreet said.

Bark beetles travel no more than a mile in most of their lifetimes, causing Overstreet to suspect that firewood haulers unwittingly imported the beetles from forests.