13: A common fungicide impairs olfactory associative learning in honey bees (Apis mellifera)

Sublethal doses of certain insecticides that target neuronal signaling have been well-demonstrated to impair the learning performance of honey bees. Honey bees are often exposed to fungicides while foraging on agricultural crops. Unlike most insecticides, fungicides target basic biochemical processes of fungal cells, and it is not clear whether they can affect learning when exposure occurs at field-relevant levels. Here, we used the proboscis extension reflex (PER) assay to test whether chronic consumption of pollen containing the fungicide Pristine^® , at a range of concentrations bracketing those measured in pollen from almond orchards, impairs olfactory associative learning in honey bees. Using a experimental design in which Pristine^® exposure occurred at larval, adult or both stages, we found that significant suppression of learning performance occurred when bees were exposed during both the larval and adult life stages. Olfactory learning performance was reduced by consumption of Pristine^® at concentrations at and above the highest concentrations of Pristine^® measured in the field, but not at doses in the lower range. Sucrose responsiveness was not affected by Pristine^®exposure, suggesting that Pristine^® does not alter hunger or motivation to seek food. Although Pristine^® is not designed to target the nervous system and has been assumed to be safe for pollinators, our study provides evidence of direct negative sublethal effects of this fungicide on olfactory learning, albeit, only with relatively high concentrations and durations of exposure. Supported by USDA 2017-68004-26322.