OF Neonics and Bees

October 14, 2019

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Written by Casey Morgan Nicholls

The systemic use of pesticides on agricultural fields poses significant risks to non-target, and often beneficial, species. Moreover, neonicotinoids applied to crop fields are taken up by birds, reptiles and invertebrates, and the pesticides often end up in aquatic systems. Although considerable research exists on the relationship between pesticide use and pollinator health, there are still knowledge gaps to be overcome, especially for wild bee species.

Three professors and a PhD student from the University of Guelph are the first to study exposure risk to pesticides in soil for ground-nesting bees. Until this point, no research has evaluated the risk to bees from neonicotinoids in soil despite the soil being where many bee species spend most of their lives. The study focused on the hoary squash bee, a solitary ground-nesting species that builds their nests in the soil of Curcubita fields and eats mainly Curcubita crop pollen and nectar.

Soil, pollen and nectar samples were gathered by Susan Chan from 18 Ontario squash farms and were analyzed to establish pesticide residue profiles. The researchers related the pesticide concentrations to honeybee lethal dose endpoints to create hazard quotients. Also, Chan et al. used honeybee and solitary bee lethal dose endpoints to develop Environmental Exposure Distributions (EED) for chronic exposure and acute exposure scenarios. Then, the same approach was used with a government data set of neonicotinoid concentrations in agricultural soil to find the exposure risk for ground-nesting bees more generally.

The results of the study indicate that significant portions of ground-nesting bee populations are likely exposed to lethal doses of neonicotinoids in Ontario agricultural fields. Out of the three exposure matrices, soil was found to have the largest number of neonicotinoids present. For the acute exposure scenario, EEDs for clothianidin and imidacloprid did not exceed the acceptable risk threshold of 5% for 2 of the 3 endpoints, but did exceed 5% for both neonicotinoids using the third endpoint. In the chronic exposure scenario, the exposure risks for clothianidin and imidacloprid exceeded 5% for all endpoints. The analysis of the secondary data set indicated high risk to ground-nesting bees from clothianidin in both exposure scenarios, and high risk for imidacloprid in chronic exposure scenarios.

Many studies that used field-realistic concentrations of neonicotinoids have brought to light the adverse effects of neonicotinoids on food collection, longevity, learning, individual navigation, resistance to disease and fecundity of honeybees. This study will hopefully prompt further research on neonicotinoids and ground-nesting bees. Chan et al. asserts that the high risk posed by clothianidin residue in soil to ground-nesting bees and other pollinators necessitates action to mitigate risks to safeguard pollinator services.

Over two-thirds of solitary bee species in eastern Canada nest in the ground and many of the species are associated with agriculture. It is well-established that the systemic use of neonicotinoids has played a significant role in the decline of pollinator health at the individual, population and community levels in recent decades. However, our understanding of neonicotinoids and their effect on wild bee species is still in its infancy due to honeybees being the main research focus. Likewise, risk assessments for pesticide impacts on pollinators are based on honeybees and so they do not currently take into account the exposure impacts from pesticides in soil. The researchers hope that the study will contribute to the restructuring of risk assessments so that ground-nesting bees can be accurately monitored.

Chan, D. S. W., Prosser, R. S., Rodriguez-Gil J. L., & Raine N.E. (2019). Assessment of risk to hoary squash bees (Peponapis pruinosa) and other ground-nesting bees from systemic insecticides in agricultural soil. Scientific Reports