Sexually dimorphic foraging is widespread among animals. In bees, for which foraging behavior and the pollination services provisioned thereby are well studied, sex-specific foraging strategies have rarely been investigated. Bees commonly exhibit sexual dimorphism in size and morphology, phenology, and life history. Furthermore, male bees do not provision offspring, and therefore do not collect and carry pollen, primarily foraging for nectar instead. Any difference between male and female bees in their choice of forage plants will have consequences for plant reproduction, plant-pollinator network structure, and on the practical side, the optimal plant species to use in pollinator habitat restorations. To determine whether male and female bees have different foraging preferences, we studied native bee species foraging in meadows in New Jersey, USA. We intensively sampled foraging bees from 6 meadow sites visited 15 times each between mid-June and mid-August, 2016. We compared the proportion of male and of female bees visiting each flower species using the Morisita-Horn dissimilarity index, and compared our results to a null model that randomized the sex identity of foragers.
We collected 8704 individual bees of 11 species from 116 flower species. As is typical of bees collected from flowers, a minority (16%) of our specimens were male. For each species, we computed the Morisita-Horn dissimilarity, which represents the relative probability that two bees of the same sex are collected from the same flower, as compared with two bees of different sexes. To account for the range of values the Morisita-Horn dissimilarity can take for the distribution of visits across flower species that we observed for each bee species, and to determine whether the non-zero values represent true differences between the sexes, we compared the Morisita-Horn dissimilarity we observed to 1000 null dissimilarities, which we computed by randomly reassigning bee sex within our dataset. For all 11 species, male and female bees had significantly different foraging preferences at alpha=0.05. The top-visited flower species were usually different for male and female bees of the same species, although there were few flowers visited at higher rates by one sex across bee taxa. Our results underline the importance of plant species diversity for supporting bee populations, and provide a window into the neglected life history of male bees.