Effect of host and larval frass volatiles on behavioural response of the old house borer, Hylotrupes bajulus (L.) (Coleoptera : Cerambycidae), in a wind tunnel bioassay

In a wind tunnel bioassay the effect of three concentrations of natural ext racts of (1) Scots pine wood, Pinus sylvestris, and (2) larval frass on the behavioural response of unmated females and males of the old house borer, Hylotrupes bajulus, was tested and compared to the behavioural effects of t he male-produced sex pheromone (3R)-3-hydroxy-2-hexanone. The influence on the behaviour of both sexes was found to be equally significant for the two higher concentrated hexane extracts of wood and larval frass. Therefore se veral synthetic monoterpenes present in the extracts and ethanol were teste d at the two higher concentrations (1:100, 1:1000 vol/vol). Among the highe r concentrated monoterpenoid hydrocarbons [(+)-alpha-pinene, (+)-beta-pinen e, (+)-limonene], only alpha-pinene increased the activity, orientation tow ards scent source and interest towards conspecifics. The tests with higher concentrated ethanol and the oxygenated monoterpenes [(-)-verbenone, (-)-tr ans-pinocarveol, (+)-terpinen-4-ol, (+)-alpha-terpineol, (-)-myrtenol] reve aled that verbenone is the most effective stimulant for the females, follow ed by trans-pinocarveol, terpinen-4-ol and alpha-terpineol. For males, terp inen-4-ol was the only mediator significantly inducing attraction and orien tation towards the scent source combined with an interest in conspecifics a pparent by fighting or courtship behaviour. Males did not respond to verben one which is a main compound of larval frass. Myrtenol and ethanol were ine ffective in both sexes. In fact behavioural observations suggest that the b eetles were repelled by the high dose of myrtenol. Using the ten-fold lower dose of the synthetic monoterpenes (1:1000 vol/vol), all semiochemicals ex cept myrtenol lost activity. Myrtenol, however, induced behavioural respons es, like increased activity and orientation towards scent source, only at t he low concentration. Based on the results, primary attraction of unmated o ld house borer is probably mediated by monoterpenes of coniferous wood, whi le secondary attraction to infested wood would occur in response to volatil es of larval frass.