Extensive pesticide usage in modern agriculture represents a considerable anthropogenic stressor to
freshwater ecosystems throughout the United States. Acute toxicity of three of the most commonly used
agricultural pesticides (Methyl Parathion
4ec, Tempo
SC Ultra, Karmex
DF, and DDT) was determined
in two different wild-caught strains of the fairy shrimp Thamnocephalus platyurus. Fairy shrimp collected
from playas surrounded by native grasslands were between 200% and 400% more sensitive than fairy
shrimp derived from playas in agricultural watersheds for Methyl Parathion
4ec, Tempo
SC Ultra, and
Karmex
DF, likely due to the development of resistance. Additionally, reduced sensitivity to DDT was
observed among fairy shrimp from agriculturally-impacted playas as compared to those from native
grassland-dominated playas. These data suggest that fairy shrimp inhabiting playas in agricultural
regions have developed some degree of resistance to a variety of agrochemicals in response to historical
usage.