Imidacloprid and acetamiprid synergistically downregulate spaetzle and myD88 of the Toll pathway in haemocytes of the European honeybee (Apis mellifera)

Pollinator health has been of critical concern over the last few decades. The prevalence of the honeybee Colony Collapse Disorder (CCD), changing climate, and the rise of vector-borne honeybee diseases by Varroa destructor, have played a major role in the rapid decline of global honeybee populations. Honeybees are environmentally and economically significant actors in biodiversity. The impact of agricultural practices, such as pesticide use, has exacerbated the negative effects on honeybees. We demonstrate the synergistic effect of cocktails of the neonicotinoids imidacloprid and acetamiprid on honeybee haemocytes. Two genes responsible for critical immune responses, spaetzle and myD88, are consistently dysregulated following exposure to either neonicotinoid alone or as a mixture with or without an immune challenge. The 2018 ban of neonicotinoids in Europe, followed by the 2020 reauthorisation of imidacloprid in France and the current consideration to reinstate acetamiprid underscores the need to evaluate their cumulative impact on honeybee health.