Seasonal variability in physiology and behavior affect the impact of fungicide exposure on honey bee (Apis mellifera) health

Authors: FISHER, A. - Arizona State University; GLASS, JORDAN - Arizona State University; OZTURK, C. - Arizona State University; DESJARDINS, N. - Arizona State University; RAKA, Y. - Arizona State University; DeGrandi-Hoffman, Gloria; SMITH, B. - Arizona State University; FEWELL, J. - Arizona State University; HARRISON, J. - Arizona State University

Submitted to: Environmental Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2022
Publication Date: 8/21/2022
Citation: Fisher, A., Glass, J.R., Ozturk, C., DesJardins, N., Raka, Y., Hoffman, G.D., Smith, B.H., Fewell, J.H., Harrison, J.F. 2022. Seasonal variability in physiology and behavior affect the impact of fungicide exposure on honey bee (Apis mellifera) health. Environmental Pollution. 311. Article 120010. https://doi.org/10.1016/j.envpol.2022.120010.
DOI: https://doi.org/10.1016/j.envpol.2022.120010

Interpretive Summary: Honey bees are lynch pins in the production of numerous fruit, vegetable and seed crops that rely on them for pollination. Exposure to agricultural plantings can cause contact with pesticides. The effects of a pesticide however, might vary depending upon the seasonal cycle of the colony. Pesticide effects, especially if they originate from the consumption of pollen and nectar, might vary seasonally. For example, in the spring and summer, colonies are expanding and consuming large amounts of pollen to rear brood. Pesticides might have greater effects when colonies are expanding than in the fall when brood rearing is slowing and less pollen is being consumed. However, contaminated pollen might be stored for the winter so that bees exhibit the effects of exposure the following spring. Of the all the pesticides that honey bees might be exposed to, fungicides are the most common because they can be applied during crop bloom. The mechanisms by which fungicides affect honey bees are poorly understood and seasonal variations in their impact have not been explored. We assessed the effects of a four-week exposure of the fungicide, Pristine® on honey bee colonies by feeding them pollen patties containing the fungicide in either summer or fall. We measured colony brood and worker populations, pollen collection and consumption, worker age of first foraging and longevity. During the summer, Pristine® exposure induced foraging by younger workers, and reduced worker longevity resulting in smaller colonies. During the fall, Pristine® exposure again induced precocious foraging but otherwise had no significant effects. Fungicides and other pesticides may have less impact on honey bees during seasons of reduced colony growth because bees are consuming less pollen and pesticide. In our study though, pollen was not stored in the colony, so we could not assess the impact on the overwintering population though this should be considered when measuring the impact of fall exposure to pesticides.

Technical Abstract: Honey bee pollination services are of tremendous agricultural and economic importance. Despite this, honey bees and other pollinators face ongoing perils, including population declines due to a variety of environmental stressors. Fungicides may be particularly insidious stressors for pollinators due to their environmental ubiquity and widespread approval for application during crop bloom. The mechanisms by which fungicides affect honey bees are poorly understood and any seasonal variations in their impact are unknown. Here we assess the effects on honey bee colonies of four-week exposure (the approximate duration of the almond pollination season) of a fungicide, Pristine ® (25.2% boscalid, 12.8% pyraclostrobin), that has been commonly used for almonds. We exposed colonies to Pristine ® in pollen patties placed into the hive, in either summer or fall, and assessed colony brood and worker populations, colony pollen collection and consumption, and worker age of first foraging and longevity. During the summer, Pristine ® exposure induced precocious foraging, and reduced worker longevity resulting in smaller colonies. During the fall, Pristine ® exposure induced precocious foraging but otherwise had no significant measured effects. During the fall, adult and brood population levels, and pollen consumption and collection, were all much lower, likely due to preparations for winter. Fungicides and other pesticides may often have reduced effects on honey bees during seasons of suppressed colony growth due to bees consuming less pollen and pesticide.