Uptake and toxicity of clothianidin to monarch butterflies from milkweed consumption (ver. 2.0, January 2020)

Recent concern for the adverse effects from neonicotinoid insecticides has centered on risk for insect pollinators in general and bees specifically. However, natural resource managers are also concerned about the risk of neonicotinoids to conservation efforts for the monarch butterfly (Danaus plexippus) and need a tool to estimate risk for wild monarch butterflies exposed to clothianidin. In the present study, monarch butterfly larvae were exposed to contaminated milkweed plants from hatch until pupation, and the effects upon larval survival, larval growth, pupation success, and adult mass were measured. Soils dosed with a granular insecticide product lead to average clothianidin concentrations of 10.8 - 843 ng/g in milkweed leaves, 5.8 - 58.0 ng/g in larvae, and 2.6 - 5.1 ng/g in adult butterflies. The estimated LC50 for total mortality from consumption of milkweed leaves was 47 ng/g (29.3 - 75.8). Lastly, larval growth rate declined as clothianidin concentrations in leaves increased.