Non-pathogenic immune challenge negatively affects chill coma recovery and thermal tolerance in the bumble bee Bombus impatiens

How environmental stressors such as pathogens affect thermoregulatory and thermal tolerance traits in bumble bees is poorly understood. We hypothesized that a challenge to the bumble bee immune system may negatively affect these traits due to the energy investments required for immune responses and maintenance of thermal homeostasis. Bumble bee workers exposed to a 24 h, non-pathogenic immune challenge (i.e., heat-inactivated bacteria) demonstrated significantly reduced thoracic temperature during recovery from chill coma and significantly reduced tolerance to exposure to temperatures ≥ 40 °C compared to bees in control groups. In addition, immune challenged bees were in poorer conditions that control group bees when allowed to recover from heat tolerance assays for 4 h. The 24 h immune challenge did not affect body total lipid content of head, thorax and abdomen available to worker bees prior to the chill coma recovery and heat tolerance assays. We discuss our findings in the contexts of bumble bee colony health and broad extrapolation of laboratory findings to natural systems.