Comparison of Volatile Compounds and Stridulation Emitted by the Douglas-fir Beetle from Idaho and Western Oregon Populations 12

Abstract

Volatile compounds were trapped from live Dendroctonus pseudotsugae from coastal (W. Oregon) and interior (Idaho) populations and analyzed by GC/MS. Two new compounds were partially characterized: pent-3-en-1-ol, found in all fed females, and 6- or 4-methylhept-5-en-2-one, identified from interior unfed males and fed females and from coastal females cross-fed in interior logs. In bioassay in Oregon, the trans isomer of the former compound increased aggregation of flying beetles to host compounds and to frontalin, and the 6-methyl isomer of methylheptenone effected 74% inhibition of flight aggregation. Fed Idaho females released a greater quantity of frontalin, but the ratio of pheromones was similar in the 2 populations. Unfed beetles from both populations released several monoterpenes, confirming a previous report. More β-pinene was released by interior than coastal females. Toothstrike rates of Idaho male stridulations were faster, as expected from the smaller size of interior beetles, but the general form and envelope of attractant, premating, and rivalry chirps were the same in the 2 populations. The release of methylheptenone by interior males and fed females, and greater amounts of frontalin and β-pinene by interior fed females are the most striking differences noted between the 2 populations studied; however, cross-feeding tests indicated that this difference is probably host-determined rather than genetic.