Phenology leads to different wild bees with different traits pollinating spring- and summer-blooming crops

Wild bees are crucial crop pollinators, but our ability to manage this ecosystem service is limited by lack of attention to which wild bee species are key pollinators of which crops. Flower visitation to a given crop is typically dominated by just a few bee species, and this information could be used to develop targeted, crop-specific management. To identify the dominant wild bees visiting crops in northeastern North America, we compiled 29 datasets of wild bee visits to crop flowers. We summarized the identities and traits of dominant wild bees in each dataset and evaluated how the taxonomic and functional composition of wild bee visitors shifted with the season in which a crop bloomed. Of 265 wild bee species observed on crops, we identified 52 dominant species, defined as species providing ≥5% of visits to at least one crop. On average across datasets, dominant visitors comprised only 16% of the observed bee species yet performed 71% of crop visitation. Critically, the dominant bee species differed between crop species, and much of the variation in dominant species identities and functional traits was explained by phenology. In our study region, wild bee crop visitation broadly shifted from a spring suite of solitary, soil-nesting species with short flight seasons, to a summer suite of social species with long flight seasons. Thus, targeted pollinator management strategies should differ between spring- and summer-blooming crops to meet the resource needs of these distinct sets of species, with particular attention to conserving and restoring habitats that provide floral resources throughout the flight seasons of the dominant visitors. While our particular findings are specific to our study region, phenological turnover of wild bee communities is a general phenomenon that is likely to be useful for informing targeted pollinator management in other regions as well.