Selenium Toxicity to Honey Bee (Apis mellifera L.) Pollinators: Effects on Behaviors and Survival

Abstract

We know very little about how soil-borne pollutants such as selenium (Se) can impact pollinators, even though Se has contaminated soils and plants in areas where insect pollination can be critical to the functioning of both agricultural and natural ecosystems. Se can be biotransferred throughout the food web, but few studies have examined its effects on the insects that feed on Se-accumulating plants, particularly pollinators. In laboratory bioassays, we used proboscis extension reflex (PER) and taste perception to determine if the presence of Se affected the gustatory response of honey bee (Apis mellifera L., Hymenoptera: Apidae) foragers. Antennae and proboscises were stimulated with both organic (selenomethionine) and inorganic (selenate) forms of Se that commonly occur in Se-accumulating plants. Methionine was also tested. Each compound was dissolved in 1 M sucrose at 5 concentrations, with sucrose alone as a control. Antennal stimulation with selenomethionine and methionine reduced PER at higher concentrations. Selenate did not reduce gustatory behaviors. Two hours after being fed the treatments, bees were tested for sucrose response threshold. Bees fed selenate responded less to sucrose stimulation. Mortality was higher in bees chronically dosed with selenate compared with a single dose. Selenomethionine did not increase mortality except at the highest concentration. Methionine did not significantly impact survival. Our study has shown that bees fed selenate were less responsive to sucrose, which may lead to a reduction in incoming floral resources needed to support coworkers and larvae in the field. If honey bees forage on nectar containing Se (particularly selenate), reductions in population numbers may occur due to direct toxicity. Given that honey bees are willing to consume food resources containing Se and may not avoid Se compounds in the plant tissues on which they are foraging, they may suffer similar adverse effects as seen in other insect guilds.

Cadmium and Selenate Exposure Affects the Honey Bee Microbiome and Metabolome, and Bee-Associated Bacteria Show Potential for Bioaccumulation

“…As tetrasaccharides are common storage carbohydrates in plants (90) and as we fed a soy-based pollen substitute to the bees, the reduction of tetrasaccharide levels in toxicant-exposed bees may have been due to treatments causing bees to decrease diet consumption. While honey bees are not known to be able to detect cadmium or selenate in their diet (55,91), the chronic effects of sublethal toxicant exposure on the gustatory response of honey bees are unknown and should be assayed in future experiments. Coumaric acid is involved in upregulating detoxification genes in honey bees (75), but its metabolites are unknown, so the "coumaric acid-like" compound that we detected may be part of the bees' metabolism or may have come directly from their diet.…”

The bumble bee microbiome increases survival of bees exposed to selenate toxicity

“…Likewise, Hladun et al found that honey bees ( Apis mellifera ) readily foraged on Raphanus sativus plants that were grown in seleniferous soil and collected pollen containing up to 2830 mg kg −1 selenium (Hladun et al, ). Accumulating selenium in the tissues of foraging honey bees has been shown to be detrimental to both the individual forager bees plus the health of the whole colony (Hladun et al, ; ; ). Metals may also have sub‐lethal effects on bees, as foraging efficiency is decreased when honey bees are exposed to manganese (Sovik et al, ) and bumble bees are exposed to nickel (Meindl and Ashman, ; ).…”

Ecological Importance of Insects in Selenium Biogenic Cycling

“…In addition, reduced ability of bees consuming selenate to eat sucrose is observed. Ultimately, effects on survival and foraging behavior may significantly reduce the productivity and longevity of the bee colony and therefore decrement pollination efficiency [35,36]. Additionally, the results of the above studies suggest that trophic transfer via pollen and nectar to insect pollinators is an important route of Se movements in the food webs.…”

“…Therefore decline of bees' population may have substantial environmental consequences. Recent studies [35][36][37] have shown that except pesticides and metals [38][39][40] Se may also be the reason for it. A well-known ecological law of optimum supposes that Se at certain concentrations may promote bee health or may become toxic if ingested in excess.…”