Emergence dynamics and host-parasite associations in a large aggregation of Andrena regularis (Hymenoptera: Apoidea: Andrenidae)

Abstract Ground-nesting solitary bees play a vital role in pollination, yet many aspects of their nesting ecology remain understudied, including population dynamics and interactions with brood parasites. We used emergence traps to estimate population size, emergence dynamics, sex ratio, and brood parasitism in a large aggregation of the ground-nesting solitary bee Andrena regularis Malloch at East Lawn Cemetery in Ithaca, NY. Over the course of the study, conducted from March 30th through May 16th, 2023, we collected 3251 individuals representing 16 species of bees, flies, and beetles, with A. regularis being the dominant species. Using emergence trap capture data over a 41-day emergence period, we document emergence phenology, sex ratio, and parasitism rate for A. regularis and its most abundant brood parasite, Nomada imbricata Smith. Our results provide insights into the population size, sex ratio, and timing of male and female emergence in a solitary, ground-nesting bee and its brood parasites. Our study demonstrates the effectiveness of emergence traps for studying existing ground-nesting bee populations. This study contributes to our knowledge of bee ecology and emphasizes the potential importance of cemeteries as refugia for ground-nesting bee populations.