Investigations of the effects of runoff from pesticide sprayed fields on survivorship of the larvae of the grass shrimp Palaemonetes pugio are described. Gravid shrimp were held in cages in the surface waters of two estuarine creeks; one creek received runoff from fields sprayed with the pesticides permethrin and thiodicarb while the other creek received runoff from an unsprayed forested area. Larvae released from field-exposed shrimp were reared in the laboratory in runoff water from the farm, from forest drainage, and in control water. Permethrin was undetectable (< 1 ng/sample) in all water except in one replicate of farm runoff. Survivorship was high (75-94%) in all treatments except for larvae reared in farm runoff water (27-35%). In a second experiment three weeks after pesticide application, survivorship was high (94-98%) in all treatments. The study concludes that runoff from agricultural fields sprayed with pesticides applied in accordance with labeled instructions can significantly reduce survivorship of larval grass shrimp, although cause of mortality is unknown.

"EPA 600/D-91/117." Microfiche.