Comparative analysis of the life cycles of solitary bees

Decreases in bee abundance and range are well documented, and will likely have severe impact worldwide on human food security, ecological communities, and economic systems. Despite the ecological and economic importance of bees, the life cycles of most are unknown. As a result, few quantitative models of the population demographics of bees exist, and those that do mostly focus on European honey bees. Due to this information gap, the most vulnerable life stages for all bee species, save one, are nearly unknown, as are the management and conservation steps to be taken to improve the persistence of both captive and wild populations. We leveraged the published knowledge on agriculturally important non-Apis bee species by gathering available publications on three diverse taxa commonly used for agricultural pollination in North America: Bombus spp. (bumble bees), Osmia spp. (mason bees), and Megachile rotundata (alfalfa leaf-cutting bees). Data on survivorship and fecundity helped quantify reproductive success and the survivorship between each stage of the life cycle. Population growth rate (lambda) was quantitied, as well as the sensitivity of growth rate to each of the life cycle transitions. Vast differences among taxa are evident, so extrapolation from a single species to all others is ill-advised. Clear gaps in knowledge are evident even for these well-studied taxa. Our population models may inform efforts to further develop the taxa as crop pollinators as well as provide some insight into the life stages that should be targeted by conservation efforts in vulnerable species with similar life histories.