Upwind flight response of the bark beetle predator Thanasimus dubius towards olfactory and visual cues in a wind tunnel

1 The checkered beetle Thanasimus dubius (Fabricius) (Coleoptera: Cleridae) is a common predator in North America that feeds on bark beetles (mostly Ips and Dendroctonus spp.) (Coleoptera: Curculionidae: Scolytinae). Despite numerous field-trapping studies on this predator, the response of individual T. dubius to bark beetle pheromones, host tree volatiles and visual stimuli has seldom been studied in the laboratory. 2 We present a detailed description of T. dubius chemotactic behaviour using wind tunnel observations. We investigated the effect of a synomone, the tree volatile apinene, on the T. dubius response towards two kairomones, ipsenol and frontalin, which are, respectively, principal components of Ips grandicollis (Eichhoff) and Dendroctonus frontalis (Zimmermann) prey pheromones. We also compared the chemotactic responses of predators to vanilla (an artificial flavour) and a-pinene, and the response to black and white silhouettes presented near the volatile source. 3 The mean rate of one antennal behaviour (called 'stand up') was significantly higher when adult T. dubius were exposed to a semiochemical relative to a blank (no chemical) or to vanilla. The percentage of upwind flights (insects landing upwind and performing at least one 'stand up' antennal behaviour) was also significantly higher for semiochemical treatments. The presence of a-pinene did not increase significantly the T. dubius response to ipsenol or frontalin. Predators landed more frequently near black silhouettes but the difference was not significant. 4 Percentages of predators landing closer than 40 cm to the semiochemical source increased significantly during the second trial (43-63%), suggesting a possible effect of experience on chemotactic behaviour.