Assessing Thermal Tolerance of Infected and Uninfected Bombus impatiens to a Variable Thermal Environment



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In insect species such as the common eastern bumble bee, Bombus impatiens, the relationships between body size, temperature, and disease are closely intertwined. Given the significant selection pressure that the latter two of these stressors impose, it is critically important to understand how climate change will impact species who carry out critical ecosystem services as mean temperatures and thermal variability increase. This work assesses the ecophysiology of B. impatiens in a simulated heatwave. It compares the thermoregulation, behavior, and metabolic rate of bumble bees when uninfected versus infected with a sublethal intestinal trypanosome, Crithidia bombi. Using a thermally controlled chamber, I measured thoracic body temperature, behavior, and respiration rates in infected and uninfected B. impatiens workers from 24 to 36 ºC. I found a significant interactive effect of infection status and body size on thermoregulation, with infection masking the side-mediated effects seen in uninfected bees. The likelihood of an individual fanning– a physiological adaptation to heat stress– increased at higher temperatures regardless of infection. Finally, the respiration rate of infected individuals demonstrated a negative relationship with infection intensity. Obtaining this fine-scale understanding of interacting stressors will provide insight on outcomes for important pollinators with respect to global climate change.



Ecophysiology, Ecology, Bumble bees, Climate change