Imperiled butterflies (Bartram’s scrub hairstreak, Florida leafwing, sawgrass skipper) in the National Key Deer Refuge (Refuge) in the Florida Keys are at risk from permethrin applied by truck-based ultra-low volume sprays for control of adult mosquitoes. Two studies that found permethrin on foliage in the Refuge indicate that spray clouds from regular spraying of adjacent residential neighborhoods are drifting into and contaminating Refuge habitat. Since imperiled butterfly species exist within those Refuge habitats, they may be at risk from the truck spraying in the adjacent neighborhoods. Dietary risk for butterflies estimated previously found the risk was likely underestimated because the measured residues probably did not represent the initial contamination level after deposition. In the current study we are estimating risk for the sawgrass skipper based on permethrin contamination on sawgrass foliage and have identified a couple of significant unknowns. First, how should exposure immediately after deposition be estimated when the contamination at a location may result from sprays occurring at multiple locations, varying distances from the sampled location, and an unknown number of days prior to sample collection? Second, how well does the permethrin concentration on leaves immediately following deposition relate to permethrin deposited onto an insect immediately after a spray? Dietary and acute contact risk were not indicated based on exposure to measured permethrin concentrations (0.51 – 57.67 ng/g ww). Published data on permethrin dissipation from plants were used to estimate permethrin concentrations on sawgrass immediately after deposition that may have occurred 21 – 358 days prior to collection and analysis of the sawgrass samples. Based on the estimated concentrations, permethrin contamination immediately after deposition at many of the sampled locations would affect butterflies. Additionally, acute contact risk would be greater than dietary risk. The increased risk likelihood from the estimated concentrations highlights the need to further investigate the identified unknowns.

Risk estimation for butterflies exposed to permethrin from mosquito control sprays

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