ORIGINAL ABSTRACT

Herbicides, including glyphosate, have negative impacts on honey bees (Hymenoptera: Apidae, Apis mellifera, Linnaeus, 1758) and bumble bees (Bombus spp., Hymenoptera: Apidae, Latreille, 1802), but no study has addressed effects on wild, ground-nesting bees in a field setting. Over a 3-yr study, we identified pairs of wild bee nest aggregations and applied a topical spray glyphosate treatment to 1 member of each pair. We excavated nests, collected bees, and performed mortality and mass comparisons between the glyphosate-treated and untreated aggregations. We collected overwintered adults to assess the effects of developmental glyphosate exposure on adult mass and body size, and we reared excavated larvae to monitor survival to adulthood and measure body mass. We recovered several species of adult Andrena (Hymenoptera: Andrenidae, Fabricius, 1775), Colletes (Hymenoptera: Colletidae, Latreille, 1802), Lasioglossum (Hymenoptera: Halictidae, Curtis, 1833), Nomada (Hymenoptera: Apidae, Scopoli, 1770), and Halictus (Hymenoptera: Apidae, Latreille, 1804), and we found no significant effects of glyphosate exposure on larval survival or the overall number of bees recovered from an aggregation. We found that adult Andrena from glyphosate-treated aggregations were larger and had greater mass than those from untreated aggregations, but found no differences in larval mass as a function of treatment. Our results suggest that developing ground-nesting bees are not at risk of mortality or loss of mass due to surface applications of glyphosate, but increased site replication, and studies at larger spatial scales, are necessary to fully understand these risks.