The impact of experimental warming on bumblebees: Higher temperatures induce behavioral changes in Bombus terrestris queens

Abstract

Bumblebees (Bombus terrestris) are important pollinators in most temperate and boreal ecosystems, but these regions are increasingly affected by heatwaves that are a symptom of anthropogenic climate change. Bumblebee queens may be particularly vulnerable to elevated temperatures during their solitary period following overwintering. Using an experimental system with numerous replicates, we investigated the oviposition behavior of overwintered spring queens, the resulting colony characteristics, and the mating behavior of newly emerged fall queens at three different temperatures: optimal (27 °C; C27), moderately high (32 °C; C32), and high (35 °C; C35). Spring queens exposed to higher temperatures exhibited unusual behavior, with spring queens in the C35 group more frequently digging up and destroying egg cells, ultimately leading to colony failure. Compared to C27, spring queens in the C32 treatment displayed more frequent ovipo sition, a higher colony formation rate, a higher number of offspring per colony, a shorter colony development period, and lower body sizes in their adult offspring. These results indicate that elevated temperatures lead to behavioral changes in spring queens and affect the characteristics of resulting colonies. Fall queens exhibited mating avoidance behavior at higher temperatures, resulting in a lower mating rate. Our results demonstrate that bumblebee queens respond to thermal condi tions that can lead to colony failure when thermal limits are exceeded. In nature, behavioral changes induced in bumblebee queens exposed to persistent heatwaves during the solitary period may be seriously deleterious to bumblebee populations in many regions.