Adult emergence order in a community of cavity-nesting bees and wasps, and their parasites

Evaluating resource use and overlap through time and space among and within species having similar habitat requirements informs community-level conservation and coexistence, efforts to monitor species at-risk and biological invasions. Many species share common nesting requirements; one example are cavity-nest bees and wasps, which provision nests in dark and dry holes in wood, plant stems, or other plant-based materials that can be bundled together into ‘trap nests’. In this study, the adult emergence order of 47 species of solitary cavity-nesting bees and wasps, and their parasites (total N>8000 brood cells) were obtained from two hundred identical trap nests set up each year (over three years) to survey these populations across Toronto, Canada and the surrounding region. All brood cells collected were reared in a growth chamber under constant warming temperature and humidity to determine species identity, and adult emergence order. This order ranged from 0 to 38 days, with all mason bees ( Osmia spp.) emerging within the first two days, and the invasive resin bee species, Megachile sculpturalis Smith significantly later than all others. Late emerging species i) exhibited significantly greater intraspecific variation in mean emergence day and ii) were significantly larger in body size, compared to early emerging species. Detailing natural history information at the species- and community-level, such as the adult emergence order of coexisting cavity-nesting bees and wasps and their parasites, can inform the timing of deployment of trap nests to support and monitor target species, and refine experimental design to study these easily-surveyed and essential insect communities.