Host Selection and Colonization by Some Spruce Bark Beetles

Abstract

Oleoresin and turpentine, obtained from resistant or susceptible spruce trees, excite equal responses of Ips typographus L., Dendroctonus micans Kug. and Hylurgops glabratus Zett. depending on insect species only. There is no significant difference between resistant and susceptible trees in turpentine composition. There in no correlation between the intensity of oleoresin odour and tree attractiveness. The explanation of primary attractiveness of odour of oleoresin or other substances is unconvincing. I. typographus beetles select weakened trees responding to a complex of stimuli including visual, some olfactory and, possibly to biophysical ones. There is no “contact” pheromone in this species. Mass aggregation of I. typographus males is caused by host stimuli. After suppressing oleoresin exudation by the males they begin to produce a frass pheromone that attracts mainly the females. D. micans has no aggregative pheromone. Perhaps, the odour of oleoresin is important in host selection by the fertilized females of this species. The factor of spruce resistance to bark beetle attack is solely oleoresin flow.