Pesticides are a possible cause of pollinator decline and honey bee colony losses experienced in several countries in recent years. In the past years, many northwest Italian beekeepers reported the presence of dead brood in field apiaries during neonicotinoid-coated maize sowing; therefore, a possible role of these insecticides was suspected. The objective of this study was to test this hypothesis. Laboratory repeated dose toxicity tests on in vitro reared larvae were carried out using thiamethoxam. The repeated treatment median lethal concentration (LC 50) and the median lethal dose (LD 50) 14 and 19 days after grafting were calculated and resulted of the same order of magnitude of realistic brood exposure under a worst-case scenario. Various sublethal effects, like brownish larvae, duplication of the pupal integument, delay in development, and deformed adults were also observed.

A b s t r a c t While observing: non-acceptance, frequent replacements, and reduced performance in honey bee (Apis mellifera ligustica) queens, we were induced to analyse a certain number of queens to detect the causes. For this purpose, 99 newly mated queens were bought from 20 Italian queen breeders. In addition, 109 older or at-the-end-of-their-career queens, that showed poor productivity, were collected from honey production hives throughout Italy. All the queens were dissected to check the status of their reproductive system and/or the presence of various anomalies and diseases. Anatomical and functional anomalies, pertaining to ovaries and spermatheca, also in association with tissue alterations and microorganisms like Nosema spp. and protozoa, were common in both newly mated and older queens, but they were more prevalent in the latter. Observed differences permitted us to highlight the causes of the reduced performance of the queens and of the colonies they originated from. The obtained information could prove useful when it comes to improving queen breeding techniques.