D3022: Timing of spring emergence varies with body size within and among bumble bee species

For insects, the timing of life history events (phenology) often depends on temperature cues. Body size often mediates insect responses to temperature, so body size may play an important role in phenology. The determinants of spring emergence of bumble bee queens are not well understood, but body size is likely important for a number of reasons. In fall, queens accumulate energy stores to fuel overwinter survival. Accumulation of fat stores prior to and depletion of fat stores during overwintering are size-dependent: larger queens accumulate relatively more lipids and have lower mass-specific metabolic rates, suggesting delayed depletion of energy stores and potentially leading to later spring emergence. To address whether timing of spring emergence correlates with body size, we captured 14 species of Bombus queens across three elevations (from 2188 to 3285m) during the 2020 growing season, weighed them, and measured intertegular width (a size metric less affected by variation in feeding and hydration state). Early emerging queens were smaller than later emerging queens both within and among species across altitude. These data suggest that body size may influence the timing of a critical life event for these crucial pollinators.