Mountain pine beetle seasonal timing and constraints to bivoltinism: a comment on Mitton and Ferrenberg (2012)

Mountain pine beetle tree colonization typically occurs in July and August, with completion of a generation one (univoltinism) or two (semivoltinism) years later. In a 2012 publication, Mitton and Ferrenberg suggested that climate change resulted in an unprecedented generation between June and September (a summer generation), with a concomitant shift to two generations in one year (bivoltinism). Although summer generations are not uncommon in this species, completion of a second generation across winter, between September and June, would be required for bivoltinism, a phenomenon not previously observed. Mitton and Ferrenberg showed that a summer generation can occur, but they failed to adequately track cohorts and provided no compelling evidence for bivoltinism. We demonstrate that a winter generation—and hence bivoltinism—would have been physiologically impossible at the high-elevation site used in Mitton and Ferrenberg due to lower thermal developmental thresholds. The mountain pine b...

山松甲虫（Mountain pine beetle）的树木定殖通常发生于7月与8月，一个世代的完成需要1年（一化性，univoltinism）或2年（二年化性，semivoltinism）。2012年的一项研究中，米顿（Mitton）与费伦伯格（Ferrenberg）提出，气候变化导致了6月至9月间出现前所未有的世代（夏季世代），并伴随一年内完成两代的转变（二化性，bivoltinism）。尽管该物种出现夏季世代并非罕见，但要实现二化性，需在9月至次年6月间跨越冬季完成第二个世代，这一现象此前从未被观测到。米顿与费伦伯格的研究证实夏季世代确实可能出现，但他们未能充分追踪同生群（cohort），也未为二化性提供确凿证据。本研究证明，由于发育热阈值（thermal developmental thresholds）较低，在米顿与费伦伯格研究所使用的高海拔样地中，冬季世代——进而二化性——在生理上是不可能实现的。山松甲……