Host tree phytochemical responses to increased temperatures are species dependent and shape eastern spruce budworm performance

Abstract

By the end of the 21st century, a 5.7ºC mean increase in global temperature is expected to occur under a high-emissions (RCP 8.5) scenario, with higher temperatures expected in boreal forest. In Canada, eastern spruce budworm (Choristoneura fumiferana [Clemens 1865]; SBW) is the most destructive biotic disturbance, defoliating millions of hectares of forest during a single outbreak. Host-insect dynamics are largely influenced by temperature driven factors and respond to heat by exhibiting changes in growth, development, and productivity. My experiment employed heated mesocosms to test the effects of three temperature treatments and two host species, balsam fir (Abies balsamea [(L.) Mill.]) and white spruce (Picea glauca [Moench] Voss) on C. fumiferana development time, pupal mass, survival, and defoliation capacity. I also measured how temperatures affected host tree phenology and phytochemistry, as well as interactions between chemical profiles and SBW life history traits. My results suggest that responses of SBW reared on white spruce were consistent with previously established thermal curves, where SBW that developed on balsam fir were not. I concluded that balsam fir chemical profiles may have negated any temperature related benefits in SBW performance, and therefore proved to be a poorer host than previously established, providing interesting insight into future C. fumiferana disturbance dynamics and subsequent management in a warming climate. Lastly, the findings also underpin the importance of further research into SBW performance on balsam fir, as these results were largely unexpected.