Differential effects of neonicotinoid insecticides on the flight performance of two butterfly species

Long-distance flight capacity is crucial for the survival of migratory insects, and disruptions to their flight potential can have significant consequences for conservation. In this study, we examined how a widely used insecticide, clothianidin (class: neonicotinoid), impacted the flight performance of two species of migratory butterflies, Danaus plexippus and Vanessa cardui. To do this, we quantified the free-flight energetics and tethered-flight velocity of the two species using flow-through respirometry and flight mill assays. Our findings show differential effects of the pesticide on the two species. Clothianidin exposure lowered the free-flight metabolic rates of V. cardui, but had no observable effect on the flight metabolic rates of D. plexippus. Additionally, our models showed that the average velocity of V. cardui during tethered flight was not affected by clothianidin exposure, whereas there was a significant effect on the average tethered-flight velocity of D. plexippus butterflies, with higher exposure levels correlating to higher average velocities. These findings indicate that clothianidin exposure has the potential to influence the flight performance of exposed butterflies, but that not all species are impacted in the same way. This highlights the need to be thoughtful when selecting flight performance assays, as the various assays test different aspects of flight physiology, and may subsequently yield divergent results.