Neonicotinoids disrupt memory, circadian behaviour and sleep

Globally, neonicotinoids are still the most used insecticides, despite their well-documented sub-lethal effects on beneficial insects. Neonicotinoids are agonists at the nicotinic acetylcholine receptors, the main mediator of synaptic transmission in the insect brain, making them highly potent neurotoxins and insecticides. Memory, circadian rhythmicity and sleep are essential for efficient foraging in many pollinating insects, and involve nicotinic acetylcholine receptor signalling. The effect of field-relevant concentrations of European Union-banned neonicotinoids: imidacloprid, clothianidin and thiamethoxam, as well as the currently unbanned thiacloprid were tested on Drosophila memory, circadian rhythms and sleep. Field-relevant concentrations of imidacloprid, clothianidin and thiamethoxam disrupted learning, behavioural rhythmicity and sleep whilst thiacloprid exposure only affected sleep. Exposure to imidacloprid and clothianidin directly affected neurophysiology, preventing the day/night remodelling and accumulation of pigment dispersing factor neuropeptide in the dorsal terminals of clock neurons. Knockdown of the neonicotinoid susceptible Dα1 and Dβ2 nicotinic acetylcholine receptor subunits in the mushroom bodies or clock neurons recapitulated the neonicotinoid like deficits in memory or circadian/sleep behaviour demonstrating that neonicotinoid effects are likely mediated in the mushroom body and clock circuitry. Disruption to learning, circadian rhythmicity and sleep are likely to have far-reaching detrimental effects on beneficial insects in the field.