The heat is on: impact of heat waves on critical thermal maxima in larvae and adults of solitary bee Osmia bicornis (Hymenoptera: Megachilidae)

Extreme temperature events, such as heat waves, are increasing in frequency, magnitude, and duration. These events are believed to contribute to pollinator decline. Critical thermal maxima (CT_max) is a key physiological trait for understanding an organism’s ecology and predicting its responses to changes in climate. In this study, we investigated whether different life stages with distinct thermoregulatory behaviors differ in their CT_max in the solitary bee Osmia bicornis, one of the most common and important pollinators in Central Europe. Additionally, we tested the influence of excessively high temperatures, heat waves, on the CT_max in Osmia bicornis. We found CT_max varied among life stages, with adults exhibiting higher CT_max than larvae. Both females and males of adult bees showed a negative correlation between CT_max and body mass. Interestingly, adult bees exposed to different heat waves during their larval stage did not exhibit significant shifts in CT_max. These results suggest that bees may have limited capacity to enhance heat tolerance in response to prior heat exposure.