The miticide thymol in combination with trace levels of the neonicotinoid imidacloprid reduces visual learning performance in honey bees (Apis mellifera)

Abstract

Despite growing concerns over the impacts of agricultural pesticides on honey bee health, miticides (a group of pesticides used within hives to kill bee parasites) have received little attention. We know very little about how miticides might affect bee cognition, particularly in interaction with other known stressors, such as crop insecticides. Visual learning is essential for foraging bees to find their way to flowers, recognize them, and fly back to the nest. Using a standardized aversive visual conditioning assay, we tested how field exposure to three pesticides affects visual learning in European honey bees (Apis mellifera ). Our pesticides were two common miticides, thymol in the commercial formulation Apiguard® and tau-fluvalinate in the formulation Apistan® and one neonicotinoid, imidacloprid. We found no effect of miticides alone, nor of field-relevant doses of imidacloprid alone, but bees exposed to both thymol and imidacloprid showed reduced performance in the visual learning assay.

Toxicity of the Pesticides Imidacloprid, Difenoconazole and Glyphosate Alone and in Binary and Ternary Mixtures to Winter Honey Bees: Effects on Survival and Antioxidative Defenses

“…Numerous studies have shown that imidacloprid (e.g., [ 112 , 113 , 114 , 115 , 116 ]) and glyphosate [ 117 , 118 , 119 , 120 , 121 , 122 ] induce adverse sublethal effects in honey bees at the behavioral and physiological levels. It is noteworthy that imidacloprid elicits sublethal effects at exposure levels for which no interaction with its primary target (the nicotinic acetylcholine receptors [ 123 ]), responsible for the lethal insecticide effect, could be expected.…”

A neonicotinoid pesticide alters how nectar chemistry affects bees

“…Thymol is one of the phytochemicals most well studied for promoting bee health (Costa et al., 2010) and is used as a miticide treatment inside honey bee colonies (Gregorc & Planinc, 2013; Imdorf et al., 1995). However, the treatments come at a cost: A recent study revealed Apis mellifera simultaneously treated with thymol and IMD performed worse on visual learning tests than bees exposed to either chemical alone (Colin et al., 2020). Thus, beyond the shortened life spans reported here, doubly exposed bees run the risk of less efficient pollination (Gegear et al., 2021).…”

Traces of a neonicotinoid pesticide stimulates activity in honey bee colonies, but not productivity

“…In Australia honey bees exposed to 5 ppb imidacloprid were found to forage at a younger age but to accumulate less food on the long term 17,18 . Additional effects that have been reported include: increased water consumption 11 , decreased foraging performance 19 , higher bee cluster temperatures 20 and reduced learning performance when mixed with another pesticide 21 . Even so, other studies have reported no individual effects at these low levels 19,22,23 .…”