Food availability and temperature regulate diapause behavior and survival in the yellow-faced bumble bee (Bombus vosnesenskii)

The cues that govern life stage transitions are important for predicting population responses to climate change, yet the precise cues insects and other organisms use remain poorly understood. For example, despite bumble bees being a widely studied taxon, no studies to date have examined cues used to initiate diapause. I conducted a factorial experiment with Bombus vosnesenskii to assess the relative importance of food availability and temperature, two potential end-of-season cues. Gynes (newly-eclosed queens, the overwintering stage) were placed in individual containers with soil substrate and either unlimited pollen and nectar (high food) or 1mL of nectar (low food). Food treatments were crossed with temperature treatments: warm (22°C day/16°C night) or cold (22°C /5°C). Gynes in high food treatments were significantly more likely to perform diapause behaviors, while temperature and its interaction with food had no effect. This result makes sense in relation to B. vosnesenskii life cycles, which appear to involve diapause before cold conditions occur in the arid West. After one month, survival was significantly higher for queens from the cold treatment. These results together suggest that abundant late season floral resources and sufficiently cold weather are likely important for diapause initiation and survival, respectively.