Green leaf volatiles disrupt and enhance response to aggregation pheromones by the ambrosia beetle, Gnathotrichus sulcatus (Coleoptera: Scolytidae)

Experiments were conducted to test the hypothesis that green leaf volatiles (GLVs) abundant in herbaceous plants and angiosperm trees, affect the response by the conifer-infesting ambrosia beetle, Gnathotrichus sulcatus (LeConte), to pheromone-baited multiple-funnel traps. A blend of four green leaf alcohols, 1-hexanol, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol, and (Z)-3-hexen-1-ol, each released at ca. 4 mg/24 h, combined with a blend of two green leaf aldehydes, hexanal and (E)-2-hexenal, each released at ca. 13 mg/24 h, reduced trap catches to levels no different from those to unbaited control traps for both sexes. Release of the green leaf alcohols, alone or in all possible binary and ternary blends revealed additive rather than synergistic disruptive effects. Only (E)-2-hexen-1-ol was active alone. Binary and ternary blends reduced trap catches 60-88%, and 80-93%, respectively. No blend was superior, demonstrating redundancy in the disruptive effect. Released together, the two green leaf aldehydes enhanced trap catches; (E)-2-hexenal alone caused a weak enhancement. A summary of known responses by 11 scolytids to GLVs revealed variations between and within species in bioactive compounds and their effect. Disruptive GLVs offer promise alone or with other compounds as forest product protectants against ambrosia beetles.