Abstract
The mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae) is a major forest pest of pines in western North America. Beetles typically undergo a one-year life cycle with larval cold hardening in preparation for overwintering. Two-year life cycle beetles have been observed but not closely studied. This study tracks cold-hardening and preparation for overwintering by adult mountain pine beetles in their natal galleries. Adults were collected in situ between September and December 2016 for a total of nine time points during 91 days. Concentrations of 41 metabolites in these pooled samples were assessed using quantitative nuclear magnetic resonance (NMR). Levels of glycerol and proline increased significantly with lowering temperature during the autumn. Newly eclosed mountain pine beetles appear to prepare for winter by generating the same cold-tolerance compounds found in other insect larvae including mountain pine beetle, but high on-site mortality suggested that two-year life cycle adults have a less efficacious acclimation process. This is the first documentation of cold acclimation metabolite production in overwintering new adult beetles and is evidence of physiological plasticity that would allow evolution by natural selection of alternate life cycles (shortened or lengthened) under a changing climate or during expansion into new geoclimatic areas.
Highlights
The mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae), is an irruptive forest insect native to western North America [1]
A spring collection was attempted when the site was again accessible following snow melt on 26 May 2017, but no living new adults could be found in a search of the area, including thorough investigation of trees previously sampled
We found that new adult mountain pine beetles form their own metabolic antifreeze compounds in response to autumn temperature cues
Summary
The mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae), is an irruptive forest insect native to western North America [1]. Cold winters–greater than two weeks at –40 ̊C–are thought to have limited the scope of previous outbreaks by killing off mountain pine beetle brood by freezing [5,6]. Climate change has led to a warming trend in the past 30 years, reducing the length and frequency of reaching and sustaining this temperature threshold [7]. This trend is the case in the early- and late-winter season when overwintering insects would.
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