The effects of oxidative stress on the development and overwintering success of the alfalfa leafcutting bee, Megachile rotundata

Insects have profound plasticity in lifespan. Individuals entering diapause have lifespans six times longer than non-diapausing individuals in temperate species. Diapause, similar to vertebrate hibernation, may reverse senescence. Metamorphosis may also have implications for aging. During metamorphosis, larval tissues are recycled and replaced by imaginal cells, which have the potential to be cellularly “younger” than the tissues they replace. Metamorphosis may provide an opportunity to dispose of damaged somatic tissues, mitigating the effects of juvenile stress on adult lifespan. To test the disposable soma hypothesis, we used paraquat to increase reactive oxygen species (ROS) in alfalfa leafcutting bee prepupae before and after overwintering. Prepupae in opened brood cells were treated topically with either paraquat or vehicle (water). We measured survival to the adult stage, mass, development time, and adult activity. Bees treated after overwintering had reduced survival at the highest and lowest doses of paraquat, suggesting intermediate levels of ROS may not be harmful. However, increased ROS prior to overwintering had a bigger impact on bee survival, with less than 50% emerging as adults at the highest doses. In bees treated with paraquat before overwintering, time to eclosion was shorter than in controls. In bees treated after overwintering, contrary to our prediction, increased ROS led to faster development than controls. Interestingly, bees treated prior to overwintering showed no effect on flight ability, suggesting that surviving bees mitigated damage from ROS. This result provides partial support for the disposable soma hypothesis and suggests diapause may reverse senescence more than metamorphosis.