The effects of tillage on ground nesting bees

Pollination by native bees is economically and ecologically vital to agroecosystems and nature. The majority of bee species in North America rear their offspring belowground. When residing in agroecosystems, physical manipulation 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 latter, in which soil disturbance is minimized. Here we investigated the effects of tillage on nest site preference by 1) deploying soil emergence traps within subplots representing Conventional and Conservation tillage types, and the Field Edge weekly from March-October 2021, and by 2) conducting biweekly nest hole surveys from March-October 2021 in those same three treatments. Results from emergence trapping showed that bee abundance was greatest in the Field Edge, followed by Conservation then Conventional tillage. Nest hole surveys revealed Conventional tillage harbored the highest average number of nests, followed by Field Edge and then Conservation tillage. Quantifying the effects of each tillage practice on bee nesting improves the ability to conserve native bee communities in agroecosystems. Differences in nesting rates determined through emergence trapping verses surveys of nest holes suggests that tillage type affects more than nest site preference alone. Due to the potential for tillage to cause bee mortality, further research is needed to address the effects of tillage type on ground nesting bee survivorship.