Negative relationships between elevated developmental temperatures and morphological traits of different castes of bumblebees (Bombus terrestris)

Climate change can negatively impact the morphology and behavior of bumblebees. In particular, it can decrease the body size of workers, thereby reducing foraging activity. However, the morphological impacts of higher developmental temperatures on different castes of bumblebees remain insufficiently understood. In this study, we investigated the effects of elevated developmental temperatures on the morphological traits of different castes of bumblebees (Bombus terrestris). We reared queens that emerged from hibernation at different developmental temperatures: optimal (constant temperature of 27 °C), moderately high (constant temperature of 32 °C), and high (35 °C; by transferring the colony from 32 °C to 35 °C after the emergence of 10 workers). The body weight, head capsule width, body width, body length, and wing length of different castes of bumblebees significantly differed at elevated developmental temperatures. The highest impact was noted on the body width and body weight of workers, body width and wing length of queens, and body length, head capsule width, and wing length of males. Among the different castes of bumblebees, workers were most impacted by elevated developmental temperatures, followed by queens and then males. In contrast, the relative ratio of wing length to body length suggested the allometry of wing length in bumblebee castes at elevated developmental temperatures. These findings indicate that elevated developmental temperatures resulting from climate change may negatively affect the morphological traits of different castes of bumblebees.