D3110: Linking temperature limitations on flight to shifts in foraging activity of wild bumble bees

Bumble bees are critical pollinators, particularly in temperate and alpine ecosystems that are in decline globally. These declines have been linked to changing climate, partly because temperature strongly affects bumble bees at multiple life stages. Particularly during the growing season when colonies are developing, workers often fly between widely dispersed flowers to gather nectar and pollen, risking exposure to harsh temperatures to acquire resources critical for colony growth. Changing temperatures may alter the foraging behavior of workers, including grounding them at extremes. Altered or reduced foraging patterns associated with thermal challenges on flight may compromise colony health and, ultimately, populations. Previous work suggests that lab-reared B. impatiens will forage in a greenhouse at ambient temperatures from 16-36 °C and that lab-reared B. terrestris fly at the same speed from 12–30 °C. A growing body of literature has documented critical thermal limits of diverse bumble bees; however, to our knowledge, little is known regarding the degree to which temperature limits flight for free-flying wild bumble bees. We measured flight initiation and duration for wild-caught bumble bees in laboratory environmental chambers to determine the direct effects of temperature on flight. We also measured daily and seasonal variation in bumble bee foraging activity with simultaneous operative temperature monitoring. Together, these data allow us to identify how changing temperatures may limit foraging activity of these critical pollinators.