Location: Honey Bee ResearchTitle: Effects of sublethal exposure of methoxyfenozide in feeding supplement on honey bee colony activity and thermoregulation Author
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2019
Publication Date: 3/28/2019
Citation: Meikle, W.G., Corby-Harris, V.L., Carroll, M.J., Weiss, M., Snyder, L.A., Meador, C.A., Beren, E.D., Brown, N.J. 2019. Effects of sublethal exposure of methoxyfenozide in feeding supplement on honey bee colony activity and thermoregulation. PLoS One. 14(3):e0204635.
Interpretive Summary: Methoxyfenozide belongs to a class of pesticides called Insect Growth Regulators because their principle action is to mimic the natural hormones that insects use for their development. Insects exposed to such pesticides have problems with development and sexual maturation, so they tend to die without producing viable offspring. Farmers like these kinds of pesticides because they tend to be very specific for insects and have low toxicity to nontarget organisms like birds and humans. However, honey bees are insects so beekeepers and farmers are also worried that the pesticides may affect bee colonies. In this study, field-relevant concentrations of methoxyfenozide were mixed with supplemental food patties, similar to patties that commercial beekeepers use. Those hives were equipped with temperature and hive weight sensors. A concentration of 500 ppb (parts per billion) was found to affect daily foraging activity, to alter the daily activity periods of the hives, and to change how the colonies control temperature. Standard measures of hive assessment, including the amounts of adult bees and brood and the weights of newly-emerged bees were not affected. Samples of the treatment patty and of bee bread (collected when the hives were assessed) showed that: 1) methoxyfenozide concentrations were about 18-60% lower in the patties than they should have been according to lab calculations; and 2) methoxyfenozide was detected in stored bee bread in small amounts (about 1-3% of the treatment patty concentration) which indicated the bees likely stored some of the patty.
Technical Abstract: Methoxyfenozide is an insect growth regulator (IGR) commonly used in agricultural to simultaneously control pests and preserve beneficial insect populations; however, its impact on honey bees in not fully understood. We conducted field and laboratory experiments to investigate bee health in response to field-relevant doses of this pesticide. Significant effects were observed in honey bee colony flight activity and thermoregulation after being treated with methoxyfenozide. Data collected indicated that hives fed 500 ppb methoxyfenozide treated pollen patty had: 1) a significantly reduced rate of daily hive weight loss due to forager departure from dawn to dusk; 2) foraging end time delayed by 17-21 minutes compared to Control; and 3) higher temperature variability during the winter. Colonies in the 125 ppb treatment group had fewer differences with the Control group, but did show a delay in the foraging end time by 30-46 minutes compared to the Control. Bee colony metrics of adult bee mass and brood surface area, and individual bee measurements of head weight, newly-emerged bee weight, and hypopharyngeal gland size were not significantly affected by the methoxyfenozide exposure levels of our experiments. An experiment conducted using the same treatment groups in the spring resulted in fewer differences among groups than did the experiments conducted in the fall. Analyses of methoxyfenozide concentrations in the treatment patty, wax, and bee bread showed that: 1) observed methoxyfenozide concentrations were about 18-60% lower than the calculated concentrations; 2) no residues were observed in wax in any treatment; and 3) methoxyfenozide was detected in stored bee bread in the 500 ppb treatment, at concentrations about 1-2.5% of the observed concentration for that treatment. These results suggest that there may be significant effects on honey bee colony behavior (and possibly health) in the field that are difficult to detect through traditional hive inspections and individual metrics.