Sublethal Acetamiprid Exposure Induces Ovarian Degeneration and HSP70/HSP90 Overexpression in Honey Bee Queens (Apis mellifera)

The health of the honey bee (Apis mellifera) is threatened by a variety of biotic and abiotic stressors, among which pesticide exposure remains a major factor. Acetamiprid is a neonicotinoid still authorized in the European Union despite the known toxic effects exerted on honey bees. To date, its impact on queens’ health remains largely unexplored although colony survival is strongly dependent on the reproductive success of the queen. In this study, we evaluated the effects of a 7-day sublethal exposure to acetamiprid (20 μg/L) on the ovarian structure using histological and immunohistochemical approaches. The histological analysis revealed structural alterations in the ovaries of exposed queens, including disorganization of the germarium and vitellarium, cytoplasmatic vacuolization in the interstitial connective tissue, oocyte degeneration and pyknotic nuclei in nurse cells, indicative of apoptosis. In addition, immunohistochemical analysis revealed increased expression of HSP70 and HSP90, indicating a disruption of cellular proteostasis and cellular stress. These findings suggest that sublethal short-term exposure to acetamiprid may directly affect the queen bee reproductive apparatus.