Proteome of Clothianidin Exposed Honey Bees Reveals a Possible Mechanism Behind Impairment of Sucrose Responsiveness

Abstract

Neonicotinoids (NNIs) are the most commonly used insecticides in the world and clothianidin, a type of NNI, is commonly found in honey bee collected pollen. Clothianidin has several negative effects on honey bee health and behaviour, but whether and how it might impact learning and memory remains unclear. Therefore, we exposed honey bee workers to a field-realistic oral dose of clothianidin for 7 days to assess their sugar responsiveness, and olfactory learning and memory using the proboscis extension response paradigm. Sugar responsiveness impacts important colony-level traits, such as onset of foraging, that help maintain colony homeostasis as well as impacts learning and memory. We then measured how clothianidin alters protein expression in the brain in an effort to understand the mechanism(s) of clothianidin's effects. Clothianidin-exposed bees had impaired sugar responsiveness, but no effect was seen on learning and memory. We identified 5069 protein groups and showed that the exposed bees had fewer detectable proteins. The exposed bees also had fewer mitochondrial respiration proteins, as well as reduced levels of nicotinic acetylcholine receptor α7 (nAChRα7) subunit (one of the targets of clothianidin) and reduced levels of acetylcholinesterase and acetylcholinesterase-2 levels. In the exposed bees, the levels of nAChRα7 subunit positively correlated with sugar responsiveness, providing evidence for a possible mechanical explanation.