RESPONSE OF DENDROCTONUS-BREVICOMIS LE-CONTE (COLEOPTERA, SCOLYTIDAE)TO DIFFERENT RELEASE RATES AND RATIOS OF AGGREGATION SEMIOCHEMICALS AND THE INHIBITORS VERBENONE AND IPSDIENOL

The response of western pine beetle, Dendroctonus brevicomis Le Conte, to different release rates of the aggregation semiochemicals (attract ants) exo-brevicomin, frontalin, and myrcene and the inhibitors verben one and ipsdienol was investigated. Release rates of verbenone ranging from 0.18 mg/24 hr to 1.2 mg/24 hr did not result in significant redu ctions in mean trap catch of D. brevicomis. In contrast, very low rele ase rates of ipsdienol (0.02-0.4 mg/24 hr) significantly reduced trap catch compared to controls. The combination of verbenone and ipsdienol , released at rates above 0.09 and 0.02 mg/24 hr, respectively, result ed in significantly lower trap catches of D. brevicomis in attractant- baited traps. Results of an experiment testing a factorial combination of different release rates of verbenone and attractants suggest that response is not ratio-specific. The response curve of D. brevicomis to the levels of verbenone was similar across all levels of attractants, while the response to equivalent ratios of attractants to verbenone w as not similar, suggesting that the behavior of the beetles is primari ly influenced by the absolute release rate of verbenone.