Evaluating the effects of tillage type on ground nesting bees

Pollination by native bees is economically and ecologically vital to agro-ecosystems and nature. The majority of bee species in North America rear their offspring below ground. When residing in agro-ecosystems, physical manipulations of the soil such as tillage in row crop systems pose a serious threat. Tillage methods vary but can generally be categorized as belonging to either a conventional or conservation tillage regime. The former is associated with high intensities of soil disturbance compared to the latter; however, conservation tillage also differs by requiring the buildup of surface residues. Here, we investigated the effects of tillage on nest site preference by intensively sampling for ground nesting bees with soil emergence traps. The sampling took place within four treatment groups: (1) Conventional tillage, (2) Conservation tillage, (3) Reduced tillage scheme, and (4) Field Edge. Soil emergence traps were deployed weekly from March-October 2021, and again from March-November 2022. Results from emergence trap collections detected no significant differences among all in-field tillage treatments; however, we observed a statistically significant difference in the probability of bee presence in the Field Edge compared to all tillage treatments. Additionally, bee collections made from the Field Edge were more diverse than all tillage treatments for both Hill Shannon and Hill Simpson indices. Our results suggest that bee nesting is diminished in cultivated fields regardless of tillage type. The implications of these results are relevant to conservation efforts aimed at mitigating the loss of bee biodiversity, especially in landscapes dominated by agricultural activity.