Distribution of residues of neonicotinoids in the hive and in bees in relation to bee health

A field study was done to search for residues of neonicotinoids in 15 honeybee hives, in 5 apiaries to determine if any bee loss or symptoms of stress were associated with such residues. The apiaries were adjacent to corn or soybean crop fields in southern Ontario, and Quebec, Canada. Samples of healthy adult bees, larvae, impaired bees with symptoms of intoxication, black bees and dead bees were analysed for acetamiprid, clothianidin, imidacloprid, thiamethoxam, and the metabolite TZNG. Neither the concentrations of the individual compounds found nor the aggregate exposures to multiple compounds were associated with any evidence of stress or bee loss. Extensive diagnostic tests were done to monitor mites and diseases, and hive weights were monitored. Viruses were frequently found in all bee sample types. Over 90% of impaired bees had viruses, but 20% or less had any of the test compounds and only at low levels (<0.05 ng/bee) of neonicotinoids. 77% of black bees had viruses but none of the test compounds was detected in these bees. Method verification, distribution of residues in the colony, assessment of hive scale results, calculation of the combined effects, implications for diagnosis, and risk assessment will be discussed.