Mexico City ? Authorities who have struggled to stop illegal logging in Mexico’s famed monarch butterfly reserve now are cutting down thousands of trees themselves to fight an unprecedented infestation of deadly bark beetles.

Biologists and park workers are racing to fell as many as 9,000 infected fir trees and bury or extract infested wood before the orange-and-black monarchs start arriving in late October to spend the winter bunched together on branches, carpeting the trees.

Environmentalists say the forest canopy of tall firs is essential to shelter the butterflies on their annual migration through Mexico, the United States and Canada. The journey is tracked by scholars and schoolchildren across North America and draws tens of thousands of tourists to the reserve, a U.N. Heritage site.

But freezing rains and cold night air can kill the monarchs at the high-altitude reserve, so the insects are threatened by a loss of trees, whether by loggers or the bark beetles.

Migration threat?

Because the migration is an inherited trait — no butterfly lives to make the round-trip — it’s not clear whether they could find another wintering ground.

Chip Taylor, a Kansas University professor of ecology and evolutionary biology and director of KU’s Monarch Watch program, said that once a beetle gets into the wood of the tree, the tree would have to be cut down, and likely taken out of the area and burned to prevent further infestation.

“These kinds of problems have been cropping up all over the world,” he said, saying the potential impact to the monarch migration was significant.

“If the whole area goes down, we’re going to lose this migration for quite a while,” he said.

Experts say insecticide is the best way to control the beetles, but that would endanger the butterflies. Instead, park officials are fighting the plague tree-by-tree.

“It is obvious that in the medium and long term, if we do not act to adapt to the changes, then there could be a serious risk” to the butterflies’ migration, said reserve director Rosendo Caro, a forestry expert. “The forest is not going to disappear, but the conditions that make up the right environment for the wintering phenomenon could disappear.”

Widespread problem

A man cuts down a tree last week in the monarch butterfly reserve near Ocampo, Mexico. After decades of trying to stop logging in Mexico’s monarch butterfly reserve, biologists and park workers are having to cut down thousands of fir trees themselves, to combat an unprecedented infestation of bark beetles they say may have been unleashed by climate change.

Beetles are devastating forests across the continent from Colorado to the Yukon, killing millions of acres of trees. In most places, the infestation is spurred by trees weakened by drought, and beetles that thrive in warmer weather. The dead trees increase the risk of forest fires, exacerbating the problem.

Bark beetles have long been present in the monarch reserve, usually attacking a few trees in the driest months of early spring, before heavy seasonal rains that normally start in May. But this year, little rain had fallen by July, and the trees were weakened. The beetles took advantage, burrowing in and robbing the trees of nutrients until they turned orange and die.

Experts are concerned because the outbreak is occurring in patches, indicating the infestation is spreading. And a Mexican government report on climate change predicts more late or delayed summer rains, with a 15 percent decline in overall rainfall between now and 2080.

If the bark beetle attacks become a regular occurrence and more trees are felled, monarch expert Lincoln Brower worries there could be more “holes in the blanket” of the tree canopy that protects the butterflies.

Diana Six, a professor of forest entomology and pathology at the University of Montana, said the best way to protect trees is to spray their bases with the pesticide Carbaryl, but “you can’t use it if you’ve got monarchs coming in, because it’s a general pesticide; it kills everything as far as insects.”

So Mexican officials face the time-consuming task of cutting down each infested tree, removing the bark, burying it under soil, and then taking away the wood to prevent the beetles from spreading. Once the butterflies are back, the work must stop.

Caro said he thinks authorities have caught the problem in time this year.

The die-off comes just as authorities were making headway against illegal logging. Since 2006, armed police have patrolled to combat logging gangs and aid for the mountain villages that dot the reserve has helped reduce tree loss.

A report by the World Wildlife Fund and Mexican environmentalists found that deforestation in the reserve declined by about 44 percent between 2005 and 2008.