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Title: Empirical, metagenomic, and computational techniques illuminate the mechanisms by which fungicides compromise bee health

Author
item Steffan, Shawn
item DHARAMPAL, PRARTHANA - University Of Wisconsin
item DIAZ-GARCIA, LUIS - University Of Wisconsin
item CURRIE, CAMERON - University Of Wisconsin
item Zalapa, Juan
item HITTINGER, CHRIS - University Of Wisconsin

Submitted to: Journal of Visualized Experiments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2016
Publication Date: 10/9/2017
Citation: Steffan, S.A., Dharampal, P.S., Diaz-Garcia, L., Currie, C.R., Zalapa, J.E., Hittinger, C.T. 2017. Empirical, metagenomic, and computational techniques illuminate the mechanisms by which fungicides compromise bee health. Journal of Visualized Experiments. https://www.jove.com/video/54631.

Interpretive Summary: Bumble bee hives are teeming with microbes, many of which facilitate the fermentation of pollen-provisions. During this fermentation, microbes enrich and preserve the pollen for bee larvae. Fungicide residues in pollen likely affect how the resident microbes (particularly fungi) are able to condition the pollen for consumption by bee larvae. The bee-fungicide issue is a growing concern among bee keepers, researchers, and farmers. Using a suite of molecular techniques, we are investigating the hypothesis that fungicide residues severely alter the microbial community of pollen, compromising pollen quality and ultimately, causing bee mortality. Impact: Cranberry growers consistently spend substantial resources on pollination services, indicating that pollination is a critical part of crop production. As with many other cropping systems, fungicides are sprayed on cranberries during bloom. This exposes commercially managed and wild bee species to fungicide residues, and this type of exposure has been associated with significant colony losses. By investigating the mechanism(s) underlying the bee-fungicide issue, we can establish causality between fungicide exposure and bee decline, thereby providing a scientific basis for policy-makers, bee-keepers, and farmers to resolve the issue.

Technical Abstract: Because disease can be devastating to crops, growers often spray fungicides as preventative measures. Unfortunately, many sprays are applied to in-bloom crops, which expose bees to fungicide residues. Generally considered “bee-safe,” fungicides are applied globally on flowering crops. However, there is mounting evidence that fungicide residues in pollen are causing bee declines (both honey and bumble bee species) through increased bee mortality and reductions in microbial activity within pollen (i.e., “entombed pollen”). Researchers have speculated that microbes play a pivotal role in the preservation and/or processing of pollen, which in turn serves as nutrition for larval bees. In the absence of the beneficial microflora, pollen may be inadequately conditioned and/or protected, depriving the young bees of essential nourishment. By altering the microbial community structure, it is likely that fungicides disrupt these microbially-mediated ecosystem services, and compromise bee health. Through a series of carefully rendered experiments, we investigate this poorly known causality between fungicide application and colony decline. Our work provides the first evidence that fungicides cause discernable deterioration in bumble bee (Bombus impatiens) colony demographics and fitness. We further our investigation via the molecular characterization of the pollen microbiome. Using field-relevant doses of fungicide residues within pollen, we examine shifts in the structural and functional architecture of microbial assemblages within bumble bee pollen. Our work has been designed to elucidate the mechanism(s) and degree to which fungicides alter the microbial composition of pollen-provisions. Thus, our findings will shed light on the indirect pathway through which fungicides cause colony declines. Disseminating such knowledge will inform bee keepers, farmers, and policy-makers on best management practice for pollinator conservation.