Data from: 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-August, with completion of a generation one (univoltinism) or two (semivoltinism) years later. In their article, Mitton and Ferrenberg (2012) 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 2nd generation across winter, between September and June, would be required for bivoltinism, a phenomenon not previously observed. Mitton and Ferrenberg (2012) 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 (2012) due to low thermal developmental thresholds. Mountain pine beetle is indeed being influenced by climate change. To address the challenges of future population outbreaks of this significant tree mortality agent, however, it is imperative to consider data describing evolved, thermally-dependent traits that serve to maintain seasonality.

山松甲虫（Mountain pine beetle）的寄主树木定殖通常发生于7—8月，其世代发育完成需1年（一化性，univoltinism）或2年（半化性，semivoltinism）。Mitton与Ferrenberg（2012）在其研究论文中提出，气候变化导致该物种在6—9月间出现前所未有的夏季世代，并伴随一年两代（二化性，bivoltinism）的种群节律转变。尽管夏季世代在该物种中并非罕见，但要实现一年两代的二化性，需完成跨冬季的第二代发育，即9月至次年6月间的世代完成，这一现象此前从未被观测报道。Mitton与Ferrenberg（2012）虽证实夏季世代可正常发生，但他们未能对种群队列进行充分追踪，也未提供二化性的确凿证据。本研究表明，在Mitton与Ferrenberg（2012）所使用的高海拔研究站点中，由于发育热阈值（thermal developmental thresholds）偏低，冬季世代（进而实现二化性）在生理上完全不可能发生。诚然，山松甲虫确实正受到气候变化的显著影响。然而，为应对这一重要树木致死性害虫未来的种群爆发挑战，我们亟需纳入考量那些经演化形成、依赖温度调控以维持季节节律的性状相关数据。