Effects of the agricultural insecticide lambda-cyhalothrin (Warrior) on mosquitofish (Gambusia affinis)

Because agricultural insecticides have potential to disrupt biological control of mosquitoes, we quantified whether an insecticide used in rice fields causes mortality of mosquitofish. Laboratory studies have shown that lambda-cyhalothrin (Warrior) is toxic to fish; however, some studies report low field toxicities of pyrethroids to fish because they degrade rapidly and adsorb to soil. We tested whether Warrior kills mosquitofish under field conditions. Replicated enclosures in a rice field were either sprayed with Warrior at 5.8 g active ingredient/ha or were untreated. Mosquitofish were either added before the spray, or 7 days later. Of those added before the spray, none survived. Most fish added 7 days later survived.