Flight Arrestment of Tethered Dendroctonus pseudotsugae and Trypodendron lineatum (Coleoptera: Scolytidae) in Response to Olfactory Stimuli1

Abstract

With an automatically recording flight mill, the flight and arrestment responses of male striped ambrosia beetles, Trypodendron lineatum (Olivier) and male and female Douglas fir beetles, Dendroctonus pseudotsugae Hopkins, were analyzed. Males of both species required pretest flight exercise before an arrestment response to female frass occurred. Analysis of the amount of flight exercise showed that freshly emerged T. lineatum required 30 minutes and D. pseudotsugae required 90 minutes of flight to release the arrestment response. Female D. pseudotsugae were not arrested to frass even after pretest flight exercise, but both males and females were arrested to Douglas-fir, Pseudotsuga menziesii , phloem tissue. Therefore, females may detect some insect-produced “masking” compound in the frass. The arrestment response is undoubtedly a key step in scolytid host selection and secondary attraction, and provides a transitional mechanism whereby the orientation response to suitable hosts or mates (or both) is terminated, and gallery construction or reproduction (or both) are initiated. Before flight, D. pseudotsugae swallowed large amounts of air. The resulting ventricular air bubble might be used by the beetle to detect adverse weather conditions via barometric pressure fluctuations.