Mating Systems of the Tree-Killing Bark Beetle Polygraphus proximus (Coleoptera: Curculionidae: Scolytinae)

Polygraphus proximus Blandford (Coleoptera: Curculionidae: Scolytinae) has caused mass mortality of fir (Abies spp. (Pinaceae)) forests across large areas of Russia in the past decade. More recently, mass mortality of A. veitchii  Lindl. due to P. proximus infestation has been reported in Japan. This bark beetle species traditionally has been considered to be polygynous because their galleries have multiple gallery arms, and because harem-polygyny is common in the tribe Polygraphini. Although the mating system(s) potentially could have a marked effect on their reproductive success and population dynamics, the reproductive behavior of the tree-killing bark beetle P. proximus has not been investigated in detail in a natural setting in Japan. We, therefore, investigated the number of males and females in a gallery and the number of gallery arms in Abies species in Japan. None of the galleries examined contained more than one male, and 57.2% of the galleries had multiple gallery arms, even though only 2.8% of the galleries contained two females. The findings showed that the typical mating system employed by P. proximus is monogyny and that this species constructs multiple gallery arms in each gallery. In addition, 70.4% of galleries in which the sex of adult beetles could be determined contained no males, and 26.6% contained no females, suggesting that P. proximus males and females re-emerge.