Permethrin Contamination of Sawgrass Marshes and Potential Risk for the Imperiled Klot's Skipper Butterfly (Euphyes pilatka klotsi)

Abstract

Nontarget effects from mosquito control operations are possible in habitats adjacent to areas targeted by ultra‐low volume (ULV) sprays of permethrin for adult mosquito control. This paper assessed the risks of permethrin exposure to butterflies, particularly the imperiled Klot's skipper, when exposed to ground based ULV sprays. Samples of larval host plant leaves (sawgrass) were collected in June (in mosquito season) and January (outside mosquito season) of 2015 from sawgrass marsh habitats of the National Key Deer Wildlife Refuge and analyzed for permethrin. Permethrin detection was higher in June (detected on 70% of samples) than in January (30%) and concentrations were significantly higher in June (geomean = 2.1 ng/g, median = 2.4) relative to January (0.4 ng/g, median = 0.2). Dietary risk for 4th – 5th instar larvae was low based on the measured residues. The AGricultural DISPersal model (v 8.26) was used to estimate permethrin residues on sawgrass following ULV sprays (deposited residues) to estimate immediate post‐spray risk. Estimated deposited residues (33 – 543 ng/g) were much higher than measured residues, which lead to higher risk likelihood for butterfly larvae immediately after ULV sprays. The difference between estimated and measured residues, and between the two risk estimations, reflects uncertainty in risk estimates based on the measured residues. Research on modeling deposited pesticide residues following ground based ULV spray is limited. More research on estimating deposited pesticide residues from truck mounted ULV sprayers could help reduce uncertainty in the risk predictions for nontarget insects like butterflies.