A beetle the size of a grain of rice may turn the whitebark pine tree into North America's most potent symbol of global warming.

Bark beetles have decimated millions of acres of pine forest from New Mexico to British Columbia, leaving landowners with no choice but to cut down up to 75 percent of the trees on their properties. Whitebark pine trees are especially prone to infestation because they've been weakened by blister rust disease, but other pines are falling prey to the beetles as well.

More than 4 million acres of pine trees have been lost in Wyoming and Colorado alone since 2006, and British Columbia has lost 33 million acres of lodgepole pine forest. Strangely, a "freak wind event" in 2006 blew mountain pine beetles, a species of bark beetle, over the Continental Divide into northern Alberta. In Colorado, the outlook is also grim: About 5 million acres of the state's lodgepole pines more than five inches in diameter will be lost in the next three to five years.

Forest directors say they're seeing "exponential growth" of the infestation, which began when warming temperatures and a decade of drought allowed the beetles to flourish. Mature trees are more at risk than younger trees, and because wildfires have been managed so successfully for so long, all the forests are roughly the same age.

The bark beetle drills a hole through the pine bark and lays its eggs inside. When the larvae hatch, they eat the cambium layer that provides nutrients to the tree and inject the tree with a fungus that stops the tree from moving sap, which could drown the larvae.

"The Latin name is Dendroctonus, which means tree killer," says Gregg DeNitto, a Forest Service entomologist in Missoula, Mont. "They are very effective."

Efforts to fight the bark-beetle infestation are under way, but the task is overwhelming. Landowners are using "aggregator pheromones" on healthy trees in an attempt to trick the insects into moving on, but that doesn't always work. They mimic the chemical scent given off by the bark beetles when the tree is full. Large, old trees can be sprayed with insecticide, but that gets expensive quickly when treating hundreds of trees.

The pine trees are an essential part of the ecosystem, providing food and shelter for countless species. Whitebark pines produce fat-rich nuts that grizzly bears depend upon to survive. The roots of these pines prevent erosion, and without them mudslides are likely as is a buildup of silt in rivers and reservoirs that nearby communities depend upon as a water source. As the trees die, the threat of catastrophic wildfires increases dramatically, hence the need to cut them down.

Now the National Resources Defense Council is seeking to get the whitebark pine added to the endangered species list in an attempt to force the government to look at options for preserving the trees. The future threat of global warming puts the whitebark pine tree at even greater risk. The Fish and Wildlife Service has 90 days to review the NRDC petition, filed Dec. 9, to determine whether the tree is threatened or endangered, and the whole process could take up to two years.