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

Authors: DESJARDINS, N.S. - Arizona State University; FISHER, A. - Arizona State University; OZTURK, C. - Arizona State University; FEWELL, J.H. - Arizona State University; DeGrandi-Hoffman, Gloria; HARRISON, J.F. - Arizona State University; SMITH, B.H. - 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 bee colony losses can occur when foraging bees encounter insecticides while collecting nectar and pollen from treated crops. Fungicides, however, are considered bee-safe and can be applied to plants in bloom. Fungicides reduce the growth of fungal cells by inhibiting basic cellular processes. However, these processes are shared by many organisms including honey bees and are critical to their health. Though the LD50 for fungicides are high, these compounds have sublethal effects on honey bees. Previous work with a fungicide that acts as a respiratory inhibitor (Pristine®) indicated deleterious effects on protein digestion and longevity of honey bees and reduced colony growth. Whether behavior, specifically learning tasks required for efficient foraging, also is affected by Pristine® is not known. To determine if Pristine® affects learning, we conducted proboscis extension reflex (PER) tests. PER is a method to measure associative learning. In our case, we measured the ability of a bee to associate a scent with a sugar reward. We found that learning ability was reduced in bees that consumed field-relevant levels of Pristine® in pollen. The greatest reductions in learning occurred in bees fed pollen with the fungicide during their larval and early adult lives. Our study provides evidence that Pristine® has significant effects on learning performance, mediated during both larval and adult stages, and could reduce the foraging and pollinating capacities of bees.

Technical Abstract: Honey bee colony losses in recent years have been partly attributed to agrochemical exposure that occurs while bees forage on treated crops. Fungicides, however, were previously considered relatively bee-safe, as they are designed to target the biochemical processes of fungal cells. 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 field-relevant levels. Recent studies have shown that consumption of field-relevant concentrations of Pristine® in pollen by honey bee colonies causes earlier foraging, increases pollen foraging, shortens worker lifespan, and reduces colony populations. The mechanisms involved, and whether Pristine® negatively affects other aspects of behavior, such as learning ability, remain unknown. 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. We also compared learning effects for bees fed Pristine® during larval versus adult stages. We found that significant suppression of learning performance occurred when bees were exposed during both larval and adult life stages. Our study provides strong evidence that Pristine® has significant sublethal effects on learning performance, mediated during both l