How will climatic warming affect insect pollinators?

Predicting the effects of climate warming on insect pollinators is challenging. Insects are small, mobile, and can be excellent thermoregulators. We describe behavioral and physiological methods to measure pollinator body temperatures in the field and biophysical modeling approaches to predict the effects of a changing climate on pollinator body temperatures. The mechanisms that pollinators use to thermoregulate, especially in response to high temperatures, are complex, vary with life stage and phylogeny, and have been examined in very few species. Eusocial insect pollinators have coordinated social mechanisms of avoiding overheating that are generally superior to individual insects, but the brood of social insects are often sensitive to thermal variation, so the fitness effects of a failure to thermoregulate are severe. Effects of warming on performance and fitness can be evaluated in the context of thermal performance curves. Warming that raises body temperatures closer to the optimal for performance will generally be beneficial, and this effect will be common for many insects during cooler parts of the day and year. Warming that raises body temperatures above the optimal temperature will generally degrade performance and fitness. Extreme heat poses many physiological challenges, including oxidative damage, protein unfolding, and nervous system shutdown. Considerable evidence suggests that insects may be able to mitigate the effects of climate warming through developmental plasticity, migration, and evolution, but many uncertainties remain. Warming effects on flowering plant fitness and the interactions between warming and other anthropogenic effects complicate predictions but are likely to add to the negative impacts.