Electrophysiological and behavioural responses of Tomicus piniperda and Tomicus minor (Coleoptera: Scolytidae) to non-host leaf and bark volatiles

Leaf and bark volatiles from non-host birches, Betula pendula Roth. and Betula pubescens Ehrh, (Betulaceae), and aspen, Populus tremula L. (Salicaceae), were tested on spring-dispersing Tomicus piniperda (L.) and Tomicus minor (Hart.) by gas chromatographic - electroantennographic detection (GC-EAD) and by attractant-baited traps in southern Sweden. GC-EAD analysis of the head-space volatiles from fresh bark chips of B. pendula revealed two green leaf alcohols, 1-hexanol and (Z)-3-hexen-1-ol, that consistently elicited antennal responses by T. piniperda and T. minor. Further analyses with synthetic mixtures showed that the antennae of these two Tomicus species also responded to other green leaf alcohols, such as (E)-2-hexen-1-ol found from the non-host leaves, and C-8-alcohols, 3-octanol and 1-octen-3-ol, from bark: of non-host bitches and aspen. No antennal responses of the Tomicus species were observed to green leaf C-6-aldehydes and C-6-acetate or to non-host bark volatiles like trans-conophthorin, benzaldehyde, salicylaldehyde, and benzyl alcohol. In field trapping experiments, blends of electrophysiologically active green leaf alcohols or C-8-alcohols resulted in reductions (>60%) in the number of T. piniperda captured compared with that for the kairomone-baited trap. When these two blends were combined, trap catch was further reduced (90%), which was not significantly different from that for the blank control. Neither the blend of two green leaf aldehydes plus the acetate nor the bark compounds trans-conophthorin or benzyl alcohol reduced trap catches, Tomicus minor had a response pattern similar to that of T. piniperda. Hylurgops palliatus (Gyll.) (Coleoptera: Scolytidae) was attracted to the combination of kairomone and verbenone but not to kairomone and was not affected by the blends of green leaf volatiles. Our results suggest that selected leaf-bath C-6-alcohols and the bark C-8-alcohols may have potential in developing semiochemical-based management programs against both pine shoot beetles by repelling them from suitable breeding and feeding sites.