Bentz Barbara J, Powell James A
USDA Forest Service, Rocky Mountain Research Station, Logan, Utah 84321.
Am Nat. 2014 Dec;184(6):787-96. doi: 10.1086/678405. Epub 2014 Nov 13.
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 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 evolved, thermally dependent traits that serve to maintain seasonality.
山地松甲虫对树木的侵害通常发生在7月和8月，一代（一年一代，即单化性）或两代（一年两代，即半化性）的发育在一两年后完成。在2012年发表的一篇文章中，米顿和费伦伯格指出，气候变化导致了在6月至9月间出现了前所未有的一代（夏季世代），同时伴随着一年出现两代（双化性）的转变。虽然该物种出现夏季世代并不罕见，但双化性需要在9月至次年6月的冬季完成第二代发育，这是之前未曾观察到的现象。米顿和费伦伯格表明夏季世代是可以出现的，但他们未能充分追踪虫群，也没有为双化性提供令人信服的证据。我们证明，由于较低的热发育阈值，在米顿和费伦伯格所使用的高海拔地区，冬季世代以及由此产生的双化性在生理上是不可能的。山地松甲虫确实受到了气候变化的影响。然而，为应对这种导致大量树木死亡的害虫未来种群爆发带来的挑战，必须考虑那些有助于维持季节性的、随温度变化而进化的特性。
