Temporal dynamics of whole body residues of the neonicotinoid insecticide imidacloprid in live or dead honeybees

In cases of acute intoxication, honeybees often lay in front of their hives for several days, exposed to sunlight and weather, before a beekeeper can take a sample. Beekeepers send samples to analytical laboratories, but sometimes no residues can be detected. Temperature and sun light could infuence the decrease of pesticides in bee samples and thereby residues left for analysis. Moreover, samples are usually sent via normal postal services without cooling. We investigated the temporal dynamics of whole-body residues of imidacloprid in live or dead honeybees following a single-meal dietary exposure of 41ng/bee under various environmental conditions, such as freezing, exposure to UV light or transfer of individuals through the mail system. Immobile, “dead” looking honeybees recovered from paralysis after 48hours. The decrease of residues in living but paralysed bees was stopped by freezing (=killing). UV light signifcantly reduced residues, but the mode of transport did not afect residue levels. Group feeding increased the variance of residues, which is relevant for acute oral toxicity tests. In conclusion, elapsed time after poisoning is key for detection of neonicotinoids. Freezing before mailing signifcantly reduced the decrease of imidacloprid residues and may increase the accuracy of laboratory analysis for pesticides.