Seasonal variability in response of Ips pini (Coleoptera: Scolytidae) to ipsdienol in New York

In May, Ips pini in New York did not respond in the field to 50-98.5% (R)-(-)-ipsdienol (synthetic). In September, beetles responded strongly to 50-60% (R)-(-)-ipsdienol (synthetic). In May and June, New York beetles showed marked preference for their own males over Arizona males, which produce an average of 94.1% (R)-(-)-ipsdienol. This suggested that ipsdienol stereochemistry alone does not ensure activity and that an additional compound is necessary for attraction in May. In the second year of field tests, attraction to synthetic ipsdienol and male beetles was tested in the spring, summer, and fall. There was response only to males in the spring and mid-summer and to both males and synthetic ipsdienol in the late summer and fall, causing a significant treatment x sampling period (date) interaction. Laboratory-reared beetles were not significantly more attracted to ipsdienol than to a blank airstream in laboratory assays, while male volatiles were significantly more attractive than ipsdienol and the blank. These data demonstrate that there is one or more unknown semiochemicals necessary for pheromonal response and that the behavioral activity of synthetic ipsdienol varies seasonally.