Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2016
Publication Date: 5/1/2016
Citation: Guseman, A.J., Miller, K., Kunkle, G., Dively, G.P., Pettis, J.S., Evans, J.D., Vanengelsdorp, D., Hawthorne, D.J. 2016. Multi-drug resistance transporters and a mechanism-based strategy for assessing risks of pesticide combinations to honey bees. PLoS One. doi: 10.1371/journal.pone.0148242.

Interpretive Summary: Annual losses of honey bee colonies remains high and combinations of pesticides, plant-produced compounds and antibiotics may cause or contribute to the losses. Even with a single stress like pesticides the combinations can be numerous and hard to test. Given that bees fly miles around their hive and can pick numerous compounds, it is very difficult to test the many different combinations bees may encounter in the environment. In this study we focused on compounds that interfere with certain biological processes associated with energy transport within cells. We used ivermectin in combination with several other compounds commonly encountered by honey bees and found it caused a change in the toxicity found that may interfered with cellular function. This mechanism-based strategy may dramatically reduce the number of tests needed to assess the possibility of adverse combinations among pesticides. This information is useful in trying to understand the role of pesticides in honey bee health.

Technical Abstract: Annual losses of honey bee colonies remain high and pesticide exposure is one possible cause. Dangerous combinations of pesticides, plant-produced compounds and antibiotics added to hives may cause or contribute to losses, but it is very difficult to test the many combinations of those compounds that bees encounter. We propose a mechanism-based strategy for simplifying the assessment of combinations of compounds, focusing here on compounds that interact with xenobiotic handling ABC transporters. We evaluate the use of ivermectin as a model substrate for these transporters. Compounds that increase sensitivity of bees to ivermectin may be inhibiting key transporters. We show that several compounds commonly encountered by honey bees (fumagillin, Pristine, quercetin) significantly increased honey bee mortality due to ivermectin and significantly reduced the LC50 of ivermectin suggesting that they may interfere with transporter function. These inhibitors also significantly increased honey bees sensitivity to the neonicotinoid insecticide acetamiprid. This mechanism-based strategy may dramatically reduce the number of tests needed to assess the possibility of adverse combinations among pesticides. We also demonstrate an in vivo transporter assay that provides physical evidence of transporter inhibition by tracking the dynamics of a fluorescent substrate of these transporters (Rhodamine B) in bee tissues. Significantly more Rhodamine B remains in the head and hemolymph of bees pretreated with higher concentrations of the transporter inhibitor verapamil. Mechanism-based strategies for simplifying the assessment of adverse chemical interactions such as described here could improve our ability to identify those combinations that pose significantly greater risk to bees and perhaps improve the risk assessment protocols for honey bees and similar sensitive species.