Honey bee foraged pollen reveals temporal changes in pollen protein content and changes in forager choice for abundant versus high protein flowers

Protein derived from pollen is an essential component of healthy bee diets. Protein content in honey bee foraged-pollen varies temporally and spatially, but the drivers underlying this variation remain poorly characterized. We assessed the temporal and spatial variation in honey bee collected pollen in 12 Michigan apiaries over 3 summers (2015–2017). We simultaneously monitored forage in flowering habitats (uncultivated floristically-rich areas and conservation program land) near these apiaries throughout the growing season. We used these data, along with data from the literature on plant pollen protein content, to determine if honey bees collected a greater proportion of pollen from plant species growing in higher abundance or from plant species that have higher protein content. Protein content in honey bee collected pollen decreased from July to September every year, and there were among-year differences in pollen protein, highlighting the temporal variation in protein collected by these insects. Pollen protein was spatially consistent and broad-scale land use categories were not correlated with pollen protein content. Rather, our findings suggest flowering habitats found across land use categories can support honey bee foraging, which may confound broader land use effects. In early July and in early September, colonies collected a greater proportion of pollen from plants that grew in greater abundance in flowering habitats, but from late July through August, a greater proportion of pollen was collected from high-protein taxa, regardless of abundance. This suggests different factors may influence pollen forager decision-making throughout the season as colony needs and/or available forage communities change. Insights into the role of plant abundance and protein content on foraging could deepen our understanding of honey bee foraging behavior and help to inform habitat restoration programs for improved honey bee nutrition outcomes.