D3353: Sensitivity of solitary bee species: Evaluation of oral toxicity of the neonicotinoid insecticide thiamethoxam to two Osmia species

Widespread insecticide use due to intensified agriculture can have long-term negative effects on bee populations. To date, most risk assessments of insecticide effects on bees focus on eusocial honey bees. This is inappropriate, given that most bee species are solitary, with substantially different life history traits that may influence their response to insecticides. The consequences of insecticide exposure can be more severe for solitary bees, as every individual actively contributes to population fitness. Thus, lethal effects on individuals inevitably affect the number of offspring produced and may ultimately lead to population decline. However, little effort has been devoted to understanding the effects of insecticides on solitary bee species.

To address this deficiency, we performed a dose-response trial with two solitary bee species – Osmia lignaria and O. cornifrons − to assess chronic toxicity (10 days) of the neonicotinoid thiamethoxam, a ubiquitous, systemic insecticide. To account for sex-specific differences, individual bees were sexed upon emergence and maintained in separate plastic cages that were equipped with a sucrose feeder used for subsequent insecticide exposure. Bees were randomly allocated to one of eight treatment groups: Control, dimethoate (1000 ppb, positive control), and six increasing thiamethoxam concentrations (range 1-1000 ppb). Mortality was recorded daily, whereas sucrose consumption was recorded every three days to calculate daily consumption and exposure. Results will be discussed in this presentation.