COS 133-1 - The influence of extreme events on the overwintering success of a major forest insect pest

Abstract: Insect pests represent a significant ecological and economic impact to forest ecosystems and natural resource management. While much research has focused on relationships and processes during the growing season, much less attention has been paid to the winter period. Extreme events, such as cold snaps and warm spells, can have significant lethal and sublethal effects. Moreover, the dynamics (e.g. timing, intensity) of these events are likely to change substantially in response to climate change. The goal of this study was to quantify the lethal and sublethal consequences of extreme warm up events on spruce budworm, the most significant defoliator of spruce-fir forests in North America. This experiment consisted of two lab-based assays that employed a temperature-controlled water bath to simulate warming events: 1) Timing Experiment - insects were subjected to a standardized warming treatment (24 hours at 10°C) during either early, mid, or late-dormancy; 2) Intensity X Duration Experiment - insects were subjected to 1 of 4 warming intensities (5, 10, 15 and 20°C) for 1 of 4 durations (6, 12, 24, and 48 hours) for a total of 16 treatment combinations.



In the Timing Experiment, exposure to warming earlier during dormancy resulted in significantly longer emergence time as well as reduced survival relative to later exposure. In the Intensity X Duration experiment, development time until pupation increased significantly in response to both increased warming duration and intensity. Moreover, we found that increased warming intensity significantly reduced spruce budworm lipid reserves. This latter result was particularly novel as the established spruce budworm paradigm suggests that lipid concentrations remain constant over the winter period. Overall, our data suggest that warming events have a significant, negative impact on spruce budworm overwintering success. Moreover, temporal context matters, with negative impacts more likely to occur when warming is experienced earlier in dormancy.