Inter-individual differences in pesticide sensitivity may trigger variability in the risk posed by
pesticides. Therefore, to better inform pesticide risk assessment for bees, we studied the variability
of responses to several pesticides based on endogenous (developmental stage, genetic background,
caste) and exogenous factors (pesticide co-exposure). We mainly investigated the toxicity of the
insecticide sulfoxaflor, the fungicide azoxystrobin and the herbicide glyphosate. We first used LD50
tests to determine the acute oral and contact toxicity of these pesticides across the different bee
species, developmental stages (larva vs adult in honey bees), castes (honey bee and bumble bee
workers, queens and drones), and genetic backgrounds (honey bee subspecies). We then considered
the risks posed by chronic and sublethal exposures to pesticides by implementing behavioural and
reproductive endpoints in the screening of pesticide toxicity.
Data showed that azoxystrobin and glyphosate under the test conditions were mildly toxic to bees.
However, a large variability in bee sensitivity to sulfoxaflor was found, especially across species and
individuals of different castes or sex. This variability is therefore important to consider for increasing
the safety margin of the risk posed by insecticides in bees. Several effects induced by sublethal
concentrations or doses of pesticides are also described, such as the occurrence of a Non-Monotonic
Dose-Response (NMDR) and delayed effects in honey bees, impairment of reproductive performances
in bumble bees, and a decreased longevity of Osmia adult females (although no effects were found
on larval development). Finally, an interaction between pesticides was found when exposure was by
contact, but not under oral exposure. In conclusion, the range of effects described here provides very
useful insights for better understanding the toxicity of pesticides and therefore the risks they might
pose to bees.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action.Prepared under contract from the European Commission; Grant agreement No. 773921; EU Horizon 2020 Research and Innovation action
