Responses to green leaf volatiles in two biogeoclimatic zones by striped Ambrosia beetle, Trypodendron lineatum

Experiments in the Coastal Western Hemlock (CWH) biogeoclimatic zone on the British Columbia (BC) coast and the Interior Douglas-fir (IDF) biogeoclimatic zone in the BC interior revealed pronounced differences in the effect of six-carbon green leaf volatiles on the response by striped ambrosia beetles, Trypodendron lineatum to multiple funnel traps baited with the aggregation pheromone lineatin. In the IDF zone, four green leaf alcohols [1-hexanol, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol, and (Z)-3-hexen-1-ol], released alone or in a quaternary blend at ca. 4 mg/24 hr/compound, caused a 63-78% reduction in trap catches. Two aldehydes, hexanal and (E)-2-hexenal, released together at ca. 13.0 mg/24 hr/compound were weakly disruptive in one of two experiments. Conversely, in the CWH zone, the two aldehydes together caused a slight, but significant, increase in the response over that to lineatin in one of two experiments, and the blend of all four alcohols caused only weak disruption of response in one of two experiments. None of the alcohols released alone was bioactive. These results may reflect adaptations that ensure accurate host location in the two ecological zones. In the CWH zone, T. lineatum attacks conifer logs almost exclusively, and surrenders the cut or broken stump habitat to Gnathotrichus spp. In the IDF zone, T. lineatum readily attacks the base of trees killed by bark beetles or fire and may utilize green leaf alcohols to detect and avoid the vertical silhouettes represented by nonhost angiosperms such as black cottonwood and trembling aspen.