An academic controversy with practical implications for risk assessment of neonicotinoids

Neonicotinoids act as neurotoxins. Whether the interactions of imidacloprid with its target site in the nervous system – the nicotinic acetylcholine receptor - is reversible or not is an academic controversy which has practical implications for the risk assessment of neonicotinoids. Some scientists argue that imidacloprid irreversibly blocks the nicotinic acetylcholine receptors. Indeed, the lethality of imidacloprid to insects appears to be dependent on the time of exposure: the longer the exposure time, the less amount of total chemical is needed to kill honeybees. However, imidacloprid and its metabolites are rapidly metabolised by detoxification enzymes in bees and a partial or full recovery from imidacloprid-induced sublethal effects on bees has been observed. In support of the reversibility-hypothesis, our data clearly indicate, that a recovery from the paralysing neurotoxic effects of a high dose of imidacloprid is possible. Strikingly, we found a non-linear dose-response relationship: the lower dose (LD50, 48h 3.7 ng/bee) had a greater impact on bee immobility/death than the higher dose of 41 ng (48 hours after ingestion).

Source: Schott M, Bischoff G, Eichner G, et al. Temporal dynamics of whole body residues of the neonicotinoid insecticide imidacloprid in live or dead honeybees. Scientific Reports. 2017;7:6288. doi:10.1038/s41598-017-06259-z.