The effectiveness of 5 tadpole shrimp (TPS) stocking rates to reduce cohorts of Culex tarsalis was studied in field microcosms (0.81-m2). Larval/pupal abundance in microcosms containing greater than 5 TPS/m2 was significantly (P less than 0.05) lower than that of controls lacking tadpole shrimp due to predation. Adult mosquito abundances captured in emergence units above the microcosms stocked with tadpole shrimp were significantly (P less than 0.05) lower than that of controls at rates greater than or equal to 10 TPS/m2. Tadpole shrimp growth during 17 days of this study was inversely proportional to their stocking rate, and a linear relationship between size and stocking rate was plotted. Tadpole shrimp stocking rates also influenced rate of mosquito development, causing significantly (P less than 0.05) shorter periods for 50% emergence where shrimp were present when compared with that of controls. Adult male Cx. tarsalis emerged significantly earlier then females in microcosms stocked at 5 TPS/m2, while no significant (P greater than 0.05) differences were detected between the sexes at the remaining predator stocking rates.