Early winter warming impacts spruce budworm (Lepidoptera: Tortricidae) energy reserves

Climate change is having a disproportionate impact on the winter period, although little is known about the implications of shifts in extreme warming events. Changes in the intensity or duration of warm-ups, for instance, may significantly influence insects given their sensitivity to temperature fluctuations. Both ecological and economic implications may be particularly pertinent for pest species such as the spruce budworm (Choristoneura fumiferana [Clem.]), the most destructive defoliator of spruce-fir forests in North America. We subjected the spruce budworm to warming events (factorial combination of 4 warming intensities and 4 durations) during the early winter dormancy phase and measured impacts on survival, development time, body condition, and biochemistry. Results suggested that survival was minimally impacted by either treatment, and there were no effects on development. Body condition varied by sex, but was similarly unaffected by warming. However, both warming treatments influenced energy reserves measured at the end of the winter period; more intense warming reduced lipid concentrations, whereas glycogen concentrations were highest at intermediate treatment levels. Overall, our findings suggest that the impacts of early winter warming events had minimal impact on insect performance. Moreover, the ultimate consequences of shifts in metabolite concentrations likely depend on their contribution to insect energetics following the resumption of development post-dormancy.