Aging in a solitary bee, Megachile rotundata, the alfalfa leafcutting bee

Adult insects can have relatively short lives, but they still may undergo senescence, age-related deterioration of an organism that leads to declines in cellular function and whole-organism performance. The mechanisms of aging, including the underlying cellular markers and performance outcomes in adult insects are not well understood for most species. To characterize senescence in an agriculturally important solitary bee, Megachile rotundata, the alfalfa leafcutting bee, we reared bees in the lab and measured walking and flight performance along with metrics of oxidative stress weekly for 4 weeks. Flight performance declined with age, with only 34% of 28-day old females and 0% of 28-day old males able to fly. Markers of oxidative damage and total antioxidant capacity increased and plateaued after the first week. To determine if the decrease in flight performance negatively affected bee fitness in the field, marked adults were released and allowed to nest. Oocyte volume and bee foraging remained high at 21 days of age. Reproduction began to decrease with fewer brood cells per nest by 28 days. Interestingly, offspring of old females were as large as those of young females and had similar survival. Together these data suggest that M. rotundata does not senesce in its first month in the field. Predation may be a bigger cause of death in the field. This is good for farmers who can rely on M. rotundata to pollinate alfalfa for a longer period of time.