Effects of a plant-accumulated pollutant on the foraging behaviors of Apis mellifera (Hymenoptera: Apidae)

Selenium (Se) from agricultural runoff has contaminated areas of the San Joaquin Valley in California where insect pollination can be critical to the functioning of both agricultural and natural ecosystems, yet we know very little about how soil-borne pollutants such as Se can impact pollinators. In greenhouse studies, two plant species (Brassica juncea and Raphanus sativus) were irrigated with selenate and accumulated up to 100 µg Se ml^-1 in the nectar and 1000 µg Se g^-1 in the pollen. In the laboratory, we used proboscis extension response (PER) to test whether honey bees (Apis mellifera L.) were deterred by Se. Antennae and proboscises were stimulated with both organic (selenomethionine) and inorganic (selenate) forms of Se that commonly occur in Se-accumulating plants. There were no significant differences in PER between Se treatments and sucrose controls at concentrations below 1000 µg Se ml^-1, suggesting bees may not be deterred by Se. We conducted a semi-field experiment using Se-treated radish (Raphanus sativus) to quantify pollen limitation, honey bee foraging visits, as well as Se concentrations in pollen loads, flowers, and bees. There were no significant differences in the duration or total number of visits between control and Se-irrigated plants. If pollinators cannot detect and avoid toxic Se compounds in the plant tissues they are foraging upon, they may suffer similar adverse effects to those reported in other insect guilds. Alternatively, Se is a micronutrient when ingested in low quantities and may have neutral to positive effects on pollinators.