Thermal Tolerance in the Cellophane Bee Colletes inaequalis Reflects Early Spring Adaptation and Is Independent of...

Colletes inaequalis Say is a univoltine, ground-nesting solitary bee and one of the first pollinators to emerge in the North American springtime. Males emerge earlier and are smaller than females. Despite its role as a pollinator of early spring wild plants and crops, the thermal ecology of C. inaequalis remains unexplored. We assessed its lower (CT_Min) and upper (CT_Max) critical thermal limits and chill coma recovery time, testing the effects of sex and body size (fresh body mass and intertegular distance, ITD). We also compared these thermal traits to those of the European honey bee (Apis mellifera), a similarly sized species active during the same season. Given that C. inaequalis males sometimes emerge before floral resources are available and that snowfall can occur after their emergence, we examined whether food deprivation and repeated or prolonged cold exposure impair their ability to recover from chill coma. We found that males and females of C. inaequalis exhibit similar thermal limits, and neither CT_Min nor CT_Max is influenced by ITD. Body mass did not affect chill coma recovery time. Colletes inaequalis was significantly more cold-tolerant but less heat-tolerant than honey bees, recovering much faster from chill coma. Repeated cold exposure significantly impacted recovery time, while food availability was the primary factor influencing male survival. These findings suggest that C. inaequalis is physiologically adapted to early spring conditions, in contrast to honey bees, which likely rely on social and behavioral mechanisms to cope with low temperatures. Our results suggest that bee communities may exhibit thermal tolerances that align with their seasonal activity periods.