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

Abstract

• Gallery length increased as the number of gallery arms in a gallery system increased. • Polygraphus proximus laid more eggs in two-armed galleries than in one- and three-armed ones. • Galleries with more than two arms did not have more eggs compared to two-armed ones. • Gallery length with no oviposition increased as the number of gallery arms increased. • The optimal number of arms (in terms of the number of eggs oviposited) might be two. 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.