Green Leaf Volatiles Interrupt Pheromone Response of Spruce Bark Beetle, Ips typographus

A synthetic mixture of nine green leaf volatiles (GLVs) including linalool was tested on antennae of Ips typographus (L.) with coupled gas chromatographic–electroantennographic detection (GC-EAD). Strong responses were found to 1-hexanol, (Z)-3-hexen-1-ol, and (E)-2-hexen-1-ol. Weak responses were recorded to (E)-3-hexen-1-ol, (Z)-2-hexen-1-ol and linalool, while hexanal, (E)-2-hexenal and (E)-3-hexenyl acetate elicited no EAD responses. In a laboratory walking bioassay, the attraction of I. typographus females to a synthetic pheromone source was significantly reduced when a mixture of the three most EAD-active GLV alcohols was added to the source. Further reduction in response was obtained when these three alcohols were combined with verbenone (Vn). In field trapping experiments, a blend of 1-hexanol, (Z)-3-hexen-1-ol, and (E)-2-hexen-1-ol reduced I. typographus trap catches by 85%, while ca. 70% reduction of trap catch was achieved by Vn or a blend of (E)-3-hexen-1-ol, (Z)-2-hexen-1-ol, and linalool. The strongest disruptive effect was found when Vn plus a blend of the three most EAD active GLV alcohols was added to the pheromone trap (95% catch reduction). Adding the blend of the three most EAD active alcohols to pheromone-baited traps significantly reduced the proportion of males captured. These three GLV alcohols were also disruptive in the laboratory and in the field when tested individually. Hexanal, (E)-2-hexenal, and (Z)-3-hexenyl acetate were inactive both in the lab and in the field. Our results suggest that these nonhost green leaf alcohols may explain part of the host selection behavior of conifer-attacking bark beetles and may offer a source of inhibitory signals for alternative management strategy for forest protection.