Sublethal exposure to neonicotinoids and related side effects on insect pollinators: honeybees, bumblebees, and solitary bees

Nowadays, there are increasing concerns about the bioavailability of neonicotinoids in the environment and possible exposure of nontarget organisms to these insecticides, their residues having been detected at different concentrations in many matrices, i.e., pollen, nectar, soil, water. Regarding the risk assessment process, there are still some information gaps about the exposure pathways and the possibility of various sublethal effects on insect pollinators. Recently, a clear rapprochement between the sublethal effects of different endpoints under laboratory conditions and field-realistic exposure level has been demonstrated. Here, we attempt to draw general portrayal about the current debate of the exposure to neonicotinoids and their impacts on pollinators. Depending on our extracted data from the published literature, we show that the lowest observed effect concentration under realistic field conditions in the most cases is higher than under laboratory conditions, which indicate that further long-term field research is required with consideration that our good understanding of the pollinators' responses to sublethal exposure should be taken into account in the future experimental design in order to establish vigorous conclusions. We review currently available information in the published literature, presenting the reports about detected residues in relation to multiple ways of exposure and their potential consequences on insect pollinators and community dynamics. Nevertheless, we attempt to classify the sublethal effects depending on the different biological levels from genes to population. Moreover, we consider the field-realistic exposure level and critically analyze the laboratory as well as field studies to specify their physiological and behavioral effects. Additionally, synergistic effects of different factors, including exposure to neonicotinoids and their hazards on bees, will find special attention.