Evaluating nesting microhabitat for ground-nesting bees using emergence traps

Nesting resources structure native bee communities and the availability of suitable nests may enhance population abundance and persistence. Nesting rates of ground-nesting bees have proven challenging to assess due to a lack of standardized methods, We quantified the abundance of ground-nesting native bees using emergence traps over a seven-month study period. We then compared specimens captured in emergence traps with pan- and net-collected specimens. We hypothesized that ground-nesting bees would be highly similar to bees found foraging within our study site. However, the species assemblage of ground-nesting bees collected from emergence traps was significantly dissimilar from the assemblages collected with aerial nets and pan traps, indicating different sampling methods target different components of the species assemblage. We then examined the importance of nesting resources found at each emergence trap on the abundance of ground-nesting bees collected from emergence traps. Quantification of potential nesting resources, such as percent bare soil, has been proposed as a proxy of nesting habitat for ground-nesting guilds. Sloped ground and soil compaction were the most predictive nesting resources at the community-level. Further, spatial distribution of nesting resources within the study landscape also affected nesting rates, although this varied by species. Bees occurred in 85% of emergence traps, with sampling date strongly affecting the number of bees collected. Emergence traps provide a useful method of sampling the ground-nesting native bee community and investigating nesting incidence.