Spring mortality in honey bees in northeastern Italy: detection of pesticides and viruses in dead honey bees and other matrices

In spring there is often a rise in honey bee mortality incidents. The aim of this study was to investigate the potential correlation, in the reported incidents, between exposure to pesticide treatments and virus infections. Here we summarize the situation in northeastern Italy during spring 2014, evaluated by monitoring 150 active ingredients and three honey bee viruses in dead honey bees and other matrices. At least one active ingredient was found in 72.2% of the 79 dead honey bee samples, with the most abundant (59.4%) being insecticides, mainly belonging to the class of neonicotinoids (41.8%), followed by fungicides (40.6%). Imidacloprid, chlorpyrifos, tau-fluvalinate, and cyprodinil were the most frequently detected active ingredients. Multiple virus infections were monitored, revealing a high prevalence of chronic bee paralysis virus (CBPV) and deformed wing virus (DWV), detected in all samples except one. 71 and 37% of the CBPV- and DWV positive samples, respectively, showed a high number of viral copies per bee (> 10(7)). This work emphasizes possible relationship between spring mortality in honey bees and pesticide treatments. Honey bee viruses could synergistically exacerbate the negative impact of pesticides on honey bee health, endangering the survival of colonies.