The effect of warm falls on the development of an insect pest : diapause in the eastern spruce budworm (Choristoneura fumiferana)

Abstract

The eastern spruce budworm (Lepidoptera: Tortricidae: Choristoneura fumiferana) overwinters as a second-instar larva. In early fall, larvae enter a dormant state known as diapause and remains dormant during winter. Yet we know little about the physiological processes governing their diapause development. Recent studies (Roe et al., 2024) suggest that temperature in early diapause affects the spruce budworm’s ability to complete diapause during winter. In this thesis, I tested the hypothesis that exposure to warmer temperatures in fall accelerates early diapause development. I predicted that developmental traits in early diapause would be differentially expressed between budworm exposed to cool or warm temperatures. To investigate the effects of temperature on early diapause, I exposed larvae to cool (10 °C) or warm (20 °C) temperatures for up to 10 weeks of fall conditions. Larvae were sampled at eight time points during these 10 weeks to measure gene expression (via transcriptomics) and survival (motility). Additionally, I performed a separate 17-day fall and 18-week winter simulation, to whether the hibernaculum—a silken, cocoon-like structure—affected budworm overwintering survival. Larval motility decreased over time, especially at warm temperatures or in the absence of the hibernaculum. Finally, I identified potential candidates for temperature-dependent gene expression during budworm diapause.