A common fungicide, Pristine®, impairs olfactory associative learning performance in honey bees (Apis mellifera)

Authors: DESJARDINS, N.S. - Arizona State University; FISHER, ADRIAN II - Arizona State University; OZTURK, C. - Arizona State University; FEWELL, JENNIFER - Arizona State University; DeGrandi-Hoffman, Gloria; HARRISON, JON - Arizona State University; SMITH, BRIAN - Arizona State University

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2021
Publication Date: 7/5/2021
Citation: Desjardins, N., Fisher, A., Ozturk, C., Fewell, J., Hoffman, G.D., Harrison, J., Smith, B. 2021. A common fungicide, Pristine®, impairs olfactory associative learning performance in honey bees (Apis mellifera). Environmental Pollution. 288. Article 117720. https://doi.org/10.1016/j.envpol.2021.117720.
DOI: https://doi.org/10.1016/j.envpol.2021.117720

Interpretive Summary: Honey bees contribute to the production of over $12 billion worth of crops, however like other pollinators, their numbers are declining. One factor that could be contributing to honey bee loss is inadvertent consumption of fungicides. Often applied during bloom, fungicides are one of the most commonly found contaminants in pollen. Fungicides are assumed harmless to honey bees even though these agrochemicals prevent fungal growth by inhibiting basic components of cellular machinery shared by all eukaryotes. We determined the effects of fungicides on honey bees by conducting a study where full-sized honey bee colonies were fed pollen containing Pristine®. This product contains two fungicides, boscalid and pyraclostrobin. Four doses were tested ranging from 0.1 to 100x of levels previously reported to occur in honey bee collected pollen from areas where Pristine® was applied. Feeding on pollen with Pristine® reduced colony adult populations in a dose-dependent manner by 20-40% with effects increasing over time. Over-winter survival also was reduced. Bees that fed on pollen with Pristine® foraged earlier and died sooner than those feeding on uncontaminated pollen. Pristine® consumption also reduced forager associative learning abilities, as measured by odor reward responses. Finally, Pristine® increased colony pollen consumption and foraging, suggesting it may interfere with protein digestion or absorption. Together, these findings suggest that fungicides can play a significant role in pollinator decline by reducing worker lifespan and negatively affecting foraging behavior. The results from this study indicate that the safety of fungicides for pollinators should be re-evaluated.

Technical Abstract: Although fungicides were previously considered to be safe for important agricultural pollinators such as honey bees, recent evidence has shown that they can cause a number of behavioral and physiological sublethal effects. Here, we focus on the fungicide Pristine® (active ingredients: 25.2% boscalid, 12.8% pyraclostrobin), which is sprayed during the blooming period on a variety of crops and is known to affect honey bee mitochondria at fieldrelevant levels. To date, no study has tested the effects of a field-relevant concentration of a fungicide on associative learning ability in honey bees. We tested whether chronic, colony-level exposure at field-relevant and higher concentrations of Pristine® impairs performance on the proboscis extension reflex (PER) paradigm, an associative learning task. Learning performance was reduced at higher field-relevant concentrations of Pristine®. The reductions in learning performance could not be explained by effects on hunger or motivation, as sucrose responsiveness was not affected by Pristine® exposure. To determine whether Pristine®‘s negative effects on learning performance were mediated at a specific life stage, we conducted a cross-fostering experiment that exposed bees to the fungicide either only as larvae, only as adults, or during both stages. We found that exposure across the entire life was necessary to significantly reduce learning performance, although non-significant reductions occurred when bees were exposed during just one stage. Our study provides strong evidence that Pristine® has significant sublethal effects on learning performance. As associative learning is a necessary ability for foraging, our results raise concerns that Pristine® could impair foraging abilities and substantially weaken colony health.