Great Basin bristlecone pine is the longest-lived non-clonal species in the world, capable of living over 5,000 years. Perhaps one of the reasons it can attain such longevity is its unique system of defense. A new study found that these trees not only repel mountain pine beetles; they also do not support the survival of the beetle’s offspring. This makes the Great Basin bristlecone pine distinct, as nearly all other pine species within mountain pine beetle’s native range in western North America have been shown to be susceptible hosts.
Over the last several decades, mountain pine beetles have attacked and killed millions of acres of pine trees. Scientists have been particularly concerned about mountain pine beetle activity at high elevations, where Great Basin bristlecone pine grows. Temperature increases at high elevations have been linked to increased mountain pine beetle attacks in other high elevation tree species, including the iconic whitebark and limber pines.
Researchers from the USDA Forest Service Rocky Mountain Research Station and Utah State University worked with collaborators from the Humboldt-Toiyabe National Forest, Dixie National Forest, and Forest Service Forest Health Protection to identify study sites where Great Basin bristlecone pine grows in mixed stands with limber pine, which is highly susceptible to mountain pine beetle. Researchers placed live mountain pine beetles in closed boxes that were attached to either Great Basin bristlecone pine or limber pine. Beetles had the option to initiate an attack on the tree, or to exit the attack box and move into a jar away from the tree. Mountain pine beetles placed on Great Basin bristlecone pine rarely attempted attacks, and often moved away from the tree. Tests were repeated on sections of cut trees and yielded the same results. These findings indicate that mountain pine beetles are repelled by Great Basin bristlecone pine, even when no other host tree options are present. The research revealed that Great Basin bristlecone pines had significantly more concentrated and diverse defense toxins than other pines.
“This is an incredible finding,” said Barbara Bentz, a co-author of the study who is a Research Entomologist with the USDA Forest Service Rocky Mountain Research Station. “Our research shows that Great Basin bristlecone pine is the only known pine species in which most mountain pine beetles die before they can complete development.”
In addition to the field research, the scientific team, which also included Erika Eidson (Idaho Department of Lands) and Karen Mock (Utah State University), also conducted follow-up laboratory experiments in which successful mountain pine beetle attacks were simulated by manually inserting live beetles into Great Basin bristlecone and limber pine logs. The beetles successfully mated and laid eggs in both tree species, and larvae were beginning to feed beneath the bark. Nearly all of these offspring died in Great Basin bristlecone pine, while surviving offspring emerged from the limber pine logs. In fact, the number of offspring that emerged from Great Basin bristlecone pine was less than the number of parent beetles that were initially inserted into the logs.
“This has implications for how we can help protect other trees,” said Bentz. “These unique defenses could be used to develop strategies to protect other high-value trees from mountain pine beetle attacks.”
The Rocky Mountain Research Station (RMRS) is one of seven regional units that make up the U.S. Forest Service Research and Development organization. The Station maintains 12 field laboratories throughout a 12 state territory encompassing the Great Basin, Southwest, Rocky Mountains, and parts of the Great Plains, and administers and conducts research on 14 experimental forests, ranges, and watersheds, while maintaining long-term databases for these areas. RMRS research is broken into seven science program areas that serve the Forest Service as well as other federal and state agencies, international organizations, private groups, and individuals. To find out more about the RMRS go to www.fs.fed.us/rmrs. You can also follow us on Twitter at www.twitter.com/usfs_rmrs.
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