Resistance and survival to extreme heat shows circadian and sex-specific patterns in A cavity nesting bee

Abstract

The pollination services provided by insects have been a crucial part of evolution and survival for many species, including humans. For bees to be efficient pollinators they must survive the environmental insults they face daily. Thus, looking into the short- and long-term effects of heat exposure on bee performance provides us with a foundation for investigating how stress can affect insect pollination. Solitary bees are a great model for investigating the effects of environmental stress on pollinators because the vast majority of insect pollinator species are solitary rather than social. One of the most pervasive environmental stressors to insects is temperature. Here we investigated how a one-hour heat shock affected multiple metrics of performance in the alfalfa leafcutting bee, Megachile rotundata. We found that a short heat shock (1hr at 45°C) can delay adult emergence in males but not females. Bee pupae were rather resilient to a range of high temperature exposures that larvae did not survive. Following heat shock (1hr at 50°C), adult bees were drastically less active than untreated bees, and this reduction in activity was evident over several days. Heat shock also led to a decrease in bee survival and longevity. Additionally, we found a connection between starvation survival after heat shock and time of exposure, where bees exposed in the morning survived longer than those exposed in the afternoon, when they would normally experience heat shock in the field. These data suggest that there is an unexplored daily/circadian component to the stress response in bees likely similar to that seen in flies, nematodes, and plants which is constitutive or preemptive rather than restorative. Taken together our data indicate that single heat shock events have strong potential to negatively impact multiple life history traits correlated with reproduction and fitness.