When does temperature limit bee flight? Identifying the missing pieces of the puzzle

Bees are the most important insect pollinators, and nearly all bee-mediated pollination depends on flight. In this Review, we identify five key 'missing pieces' of information that limit our ability to predict how abiotic factors shape bee flight performance and ecology. First, although clade strongly influences endothermy and flight temperature limits, we still know little about how phylogeny, body size and ecological traits shape thermal biology across the full diversity of bee species; most data come from temperate, northern-hemisphere Apinae. Second, because the mechanisms of thermal balance during flight have only been studied in a handful of species, and these vary, we lack a predictive understanding of when bees will be physiologically stressed by temperature during flight. Third, although some studies suggest that desiccation may limit flight more than overheating, the links between thermal balance and water regulation remain poorly understood. Fourth, we know very little about bees' capacity to respond to thermal variation through acclimation, developmental plasticity or evolutionary adaptation. Finally, we need advances in biophysical modeling to better simulate heat and water exchange in bees, including the role of cuticular structures and internal heat transfer among body regions. Filling these gaps is essential for building predictive, mechanistic models of how climate change will affect bee physiology and bee-mediated pollination services.