Maize pollen foraging by honey bees in relation to crop area and landscape context

Abstract

The increasing demand for insect pollinated crops and high recent losses of honey bee colonies raise concerns about food security. Systemic insecticides are recognized as one of the drivers of worldwide honey and wild bee declines. Particularly honey bees in agricultural environments are exposed to pesticides when they collect crop pollen and nectar. However, landscape scale studies which analyze pollen use and foraging distances of honey bees on mass-flowering crops like maize to evaluate potential exposure risks are currently lacking. In an experimental approach on a landscape scale we took advantage of intra-colonial dance communication to gather information about the location of utilized pollen resources. During maize flowering, four observation hives were placed in and rotated between 11 different landscapes which covered a gradient from low to high maize acreage. A higher frequency of dances for foraging locations on maize fields compared to other land use types shows that maize is an intensively used pollen resource for honey bee colonies. Mean foraging distances were significantly shorter for maize pollen than for other pollen origins. The percentage of maize pollen foragers did not increase with maize acreage in the landscape. The proportion of grassland area providing alternative pollen sources did not reduce the percentage of maize pollen foragers. Our findings allow estimating the distance-related exposure risk of honey bee colonies to pollen from surrounding maize fields treated with systemic insecticides. Similarly, the results can be used to estimate the exposure to transgenic maize pollen, which is relevant for honey production in European countries. Provision of alternative pollen resources within agri-environmental schemes could potentially reduce exposure risk to pesticide contaminated crop pollen.