Mosquito Control Pesticide Impacts to Butterflies: Implications for Imperiled Butterfly Conservation on a National Wildlife Refuge

Science Center Objects

USGS researchers evaluate the impact of a pesticide on two imperiled butterfly species in the Florida Keys.

National Key Deer Wildlife Refuge

National Key Deer Wildlife Refuge (Public domain)


Florida leafwing butterfly - WARC

Florida leafwing butterfly (Anaea troglodyte floridalis)

The Science Issue and Relevance: Naled has been used as a mosquito adulticide in the Florida Keys for 28 years. The Florida Keys Mosquito Control District (District) has been permitted to apply pesticides to the National Key Deer Refuge (NKDR). Areas treated include all NKDR lands adjacent to human development and serviced by primary and secondary roads. In 2006, two butterfly species found on the NKDR (Florida leafwing [Anaea troglodyte floridalis] and Bartram’s hairstreak [Strymon acis bartrami]) were classified as candidate species. Both species have experienced recent population declines and exist at only two locations (NKDR and Everglades National Park). The Klot’s sawgrass skipper (Euphyes pilatka klotis) is a species of special concern that also resides within the NKDR, and may be exposed to the various mosquito control pesticides.

Methodology for Addressing the Issue: A series of field and laboratory studies were conducted to evaluate the potential impact of the pesticide naled to butterflies on the NKDR. Laboratory studies were used to develop a model relating dose to cholinesterase activity depression and mortality for the purpose of determining naled exposure levels that would minimize risk for butterflies. The field studies utilized in-situ toxicity testing in which caged mosquitos and caged surrogate butterflies were placed at various locations within and outside of areas targeted during aerial spray missions. Monitoring studies in the sawgrass marshes have been conducted to measure permethrin resides to which the sawgrass skipper may be exposed. 

butterfly capture

Exposure cages and pesticide residue samplers on the National Key Deer Wildlife Refuge.

(Credit: Timothy Bargar, USGS - WARC)


Bartram’s hairstreak butterfly - WARC

Bartram’s hairstreak butterfly (Strymon acis bartrami)

  1. Permethrin drift from truck application routes into the habitat of an imperiled butterfly taxon. 2015. Presented at the Annual National Meeting of the Society of Environmental Toxicology and Chemistry.


butterfly pipette

Application of mosquito control pesticide to a Julia butterfly (Dryas Julia) during toxicity testing.

(Credit: Timothy Bargar, USGS - WARC)


butterflies in exposure cages

U.S. Geological Survey scientists Tim Bargar and Carla Weiser placing butterflies into an exposure cage for field studies on the National Key Deer Wildlife Refuge. (Credit: Timothy Bargar, USGS - WARC)