The Olfactory Response of Ips confusus (LeConte) (Coleoptera: Scolytidae) to the Secondary Attraction in the Laboratory

Abstract

A highly sensitive bioassay of the olfactory response of I. confusus is described. The response of beetles to air streams carrying attractants is a chemoklinotaxis but positive orientation occurs only in moving air. There is no evidence of ameno-taxis in odorless air streams or orientation to attractants in still air. Male behavior is characterized by an “area” orientation near the attractive material, an indirect approach to the source as shown by their entering adjacent air channels, and stopping frequently in the traverse during which they make klinotactic movements. The females exhibit a “point” or “straight-line” response, crawling directly to the source, rarely deviating into adjacent channels and only occasionally interrupting their approach.Bark-wood samples of ponderosa pine become attractive 4-6 hours after male beetles are introduced into preformed entrance tunnels, the peak attraction occurring between 18 and 144 hours. Frass is not attractive until 9-12 hours after introduction of males. The ratio of females to males responding positively during the peak attraction period was approximately 8:5. The level of attractiveness to females falls as the season progresses, the highest response being recorded in late May and June. Sexual maturity as judged by the appearance of motile sperm was not correlated with host feeding or the initiation of attraction. Frass of males boring in Douglas fir was unattractive to females.Attraction is initiated by male feeding in the phloem-cambial tissue of a host and is delayed until the first food has passed through the gut. The attractant appears to be associated with male excrement and may be produced, at least in part, in the hindgut.