A mechanistic framework to explain the immunosuppressive effects of neurotoxic pesticides on bees

There is growing concern that declines in some managed and wild bee pollinator populations threaten biodiversity, the functioning of vital ecological processes and sustainable food production on a global scale. In recent years, there has been increasing evidence that sublethal exposure to the neurotoxic class of insecticides (neonicotinoids) can undermine pollinator immunocompetence and amplify the effects of diseases, which have been suspected to be one of the drivers of pollinator declines. However, exactly how neonicotinoids might inhibit pollinator immunity remains elusive. Here, we put forward a mechanistic framework to explain the effects of neurotoxic pesticides on insect immunocompetence. We propose that there is a close ontogenetic connection between the cellular arm (haemocytes) of the insect immune and nervous systems and that this connection makes the immune system of pollinators and other insects inherently susceptible to interference by neurotoxins such as neonicotinoids at sublethal doses. Investigation of this connection is urgently needed to confirm the validity of this framework and develop a clear, mechanistically informed understanding of the interplay between neonicotinoids and disease ecology in pollinators. This in turn may enable us to develop strategies to mitigate impacts of neurotoxins on pollinators and/or enhance their impacts on pests. A plain language summary is available for this article.