Repellent Effects of Host Essential Oils and Limited Effects of Host Length on Tree‐Killing Bark Beetle Attacks

ABSTRACT Various mechanisms have been proposed to play a role in host selection by bark beetles. Monoterpenes released by conifer trees may constitute a common attractive habitat cue for coniferous bark beetles, whereas monoterpenes are the principal components of tree resin and are toxic to bark beetles colonizing trees. Therefore, bark beetles infesting stressed and/or dead trees may avoid materials containing high amounts of host volatile compounds, such as host tree essential oils. Bark beetles also exhibit preferences for trunk diameters of host trees. Additionally, some bark beetles create species‐specific shaped galleries, requiring certain lengths of host materials. However, although host selection linked to trunk diameter (horizontal width) is well documented, there is limited understanding of whether bark beetles recognize vertical length of host materials. We conducted field experiments in Hokkaido, Japan, and determined the effects of host essential oils, and log length on host selection by Polygraphus proximus Blandford (Coleoptera: Scolytinae), which prefers trees with small trunk diameter, and creates horizontal egg laying galleries and vertical larval galleries. Host essential oil significantly reduced P. proximus attack density, and the attack density did not differ significantly among logs of various lengths (10 cm–80 cm) of A. sachalinensis (Fr. Schmidt) Masters (Pinaceae). Our study suggests that essential oils of a host tree can perform as repellents against conifer‐infesting bark beetles, and can be useful to reduce P. proximus attacks as a pest control strategy. Our study also suggests that P. proximus does not use vertical log length as a primary cue for host selection and may attack even on the shorter logs, which are insufficient for larval development and uncommon in natural settings.