Wednesday, August 29, 2007
Majestic Ballroom (Adams Mark)

Correlation of Bark Beetle Attack to Levels of Estragole in Ponderosa Pine

Jay J. Emerick, Aaron I. Snyder, Marc A. Snyder, and Nathan W. Bower. Colorado College, Colorado Springs, CO

Mountain pine bark (MPB) beetle (Dendroctonus ponderosae) is the most important insect pest in Colorado's Ponderosa pine (Pinus ponderosa) forests. Tree mortality is hastened by beetle inoculation with various blue stain fungus species that are symbiotic with the beetles. In previous work in Pinus caribaea in Belize, we found significantly higher percentages of estragole (4-allylanisole, CAS 140-67-0) in the xylem oleoresin of trees in stands with low levels of Dendroctonus frontalis attack compared to those with high levels of attack. Individual Caribbean pine trees showed a negative relationship between the number of visible pitch tubes (an indicator of the magnitude of attack) and concentrations of estragole in the oleoresin, suggesting this compound plays a role in observed patterns of resistance to beetle attack in this species. Estragole is an antifungal and semiochemical, decreasing aggregation in D. frontalis. In work reported here, we analyzed estragole and monoterpene profiles in the xylem oleoresin of four populations of Ponderosa pine in the Pike and San Isabel National Forests using GC-MS. Significantly lower levels of estragole and (to a lesser extent) greater chemodiversity (a measure of the evenness of the monoterpene distribution) were found in trees with pitch tubes compared to control trees from the same microclimate. We believe this is the first reporting of the potential role of xylem estragole in mediating MPB beetle induced mortality in Ponderosa pine.