Dosage response to ethanol mediates host selection by 'secondary' bark beetles.
The effect of ethanol concentration on the responses of the scolytids Ips typographus, Leperisinus varius, Hylurgops palliatus and Tomicus piniperda, the xyleborins Trypodendron lineatum [Xyloterus lineatus], Xyleborus dispar, X. saxeseni [Xyleborinus saxeseni] and Xylosandrus germanus and the lymexylid Hylecoetus dermestoides to flight barrier traps baited with their respective pheromones and/or ethanol was investigated in the field in the German Democratic Republic. Ethanol of different concentrations was released at rates of 0.001-250 mg/h. The response of all 4 xyleborins, Hylurgops palliatus and Hylecoetus dermestoides increased almost linearly with an increase in ethanol concentration. However, in Tomicus piniperda, the response to host monoterpenes decreased with increasing ethanol concentrations, and the addition of ethanol to the pheromone of I. typographus led to a reduction of the response at all concentrations. In L. varius, a low concentration of ethanol resulted in a highly synergistic effect with the male pheromone exo-brevicomin, resulting in a high number of female beetles being trapped. Higher concentrations of ethanol strongly reduced this response. It was concluded that high ethanol concentrations enhance the response of non-aggressive ('secondary') scolytids and xyleborins to aggregate on host trees, but interfere with the pheromone response among aggressive species.