SD25: Emergence dynamics, sex ratio, and parasitism rates in Andrena regularis, an early spring, solitary, ground-nesting bee (Hymenoptera: Apoidea: Andrenidae)

Ground-nesting, solitary bees play a vital role in pollination, yet many aspects of their nesting ecology remain understudied, emergence dynamics, sex ratio, and interactions with brood parasites. We studied a large aggregation of a solitary, ground-nesting bee, Andrena regularis, at the East Lawn Cemetery in Ithaca, New York in the Spring of 2023. Using emergence traps, we documented the number of emerging Andrena regularis at the site, the phenology and timeline of emergence, the sex ratio of the population, and the abundance and phenology of associated brood parasites. Based on our sampling with 10 emergence traps randomly distributed across the nestsite, we estimate that up to 5.5 million adult Andrena regularis emerged at the site in just this one year. Emergence was slightly protandrous, with males emerging earlier than females, and was highly correlated with daily high temperature. We recorded a number of brood parasites, including Nomada luteoloides, conopid flies (Myopa sp.), and meloid beetles (Lytta sp.). The parasitism rate by Nomada luteoloides, the most abundant brood parasite, was low (1.4%). The overall investment sex ratio of Andrena regularis was strongly female-biased, suggesting that this population is robust and healthy. Historical collection records indicate that this aggregation may have persisted at this site for at least 90 years. Our results demonstrate the utility of emergence traps as a tool for documenting emergence phenology in solitary, ground-nesting bees, and highlight the importance of cemeteries as important refuges for aggregations of ground-nesting, solitary bees.