Reemergence and sister brood establishment in the bark beetle Polygraphus proximus (Coleoptera: Curculionidae: Scolytinae) under laboratory conditions

Reemergence and sister broods (second broods) are commonly observed in bark beetles (Coleoptera: Curculionidae: Scolytinae), particularly in species with male-initiated polygyny and female-initiated monogyny. Polygraphus proximus Blandford, a male-initiated monogynous bark beetle, is a quarantine species in the EU, which has been introduced from east Asia into both Siberia and central European Russia, causing mortality of trees across large areas of Abies sibirica forests. To clear whether P . proximus females reemerge to lay additional broods (sister broods), we observed the reproduction of reemerged females under laboratory conditions. We prepared 25 females reproducing in galleries collected by peeling the infested logs and 25 females reemerged from such logs. These females were put into the tubes vertically attached onto the surfaces of logs. Consequently, approximately 40% of both the reproducing females in galleries and the reemerged females bored into the logs and established sister broods without repeated mating. Moreover, 21% of these reproducing females established sister broods again using the same procedures, suggesting that the females can establish sister broods more than once. Our results indicated that the fecundity of P . proximus is higher than previously assumed, suggesting that its population levels can rapidly increase in weakened or dead trees, ultimately leading to the ability to attack healthy trees during the epidemic phase.