Number of gallery arms of the tree-killing bark beetle Polygraphus proximus (Coleoptera: Curculionidae: Scolytinae)

Polygraphus proximus Blandford (Coleoptera: Curculionidae: Scolytinae) is a non-aggressive monogynous bark beetle that has caused mass mortality in fir (Abies spp.) forests in the last decade. Although gallery structures made by polygynous beetles may influence their reproductive success, the gallery structure and the number of eggs laid by the monogynous tree-killing bark beetle P. proximus has not been investigated in detail in the natural setting of their native range. We, therefore, investigated the length of mother galleries of P. proximus and the number of eggs oviposited by the beetles in relation to gallery systems with different numbers of arms. The number of eggs oviposited in two-armed galleries was significantly greater than that observed in one-and three armed galleries. Additionally, the length of one-or two-armed galleries with no oviposition was significantly shorter than that in galleries consisting of more than two arms. Our data may suggest that the optimal number of arms in a gallery system (in terms of the number of eggs oviposited) was two.

Automated summary

In this study, we investigated the gallery structure and egg oviposition of the tree-killing bark beetle Polygraphus proximus in its native range. We found that galleries with two arms had significantly more eggs oviposited compared to galleries with one or three arms. Additionally, galleries with no egg oviposition were significantly shorter in length than galleries with more than two arms. Our data suggest that the optimal number of arms in a gallery system for maximum egg oviposition is two.