Abstract
Toxicity of a phenyl pyrazole insecticide, fipronil, to 4th-instar larvae of 6 species of colonized mosquitoes (Aedes aegypti, Ae. albopictus, Ae. taeniorhynchus, Anopheles quadrimaculatus, Culex nigripalpus, and Cx. quinquefasciatus) and 2 species of field-collected chironomid midges (Chironomus crassicaudatus and Glyptotendipes paripes) was evaluated in the laboratory. All mosquito species were highly susceptible with 48-h median lethal concentration (LC50) values ranging from 0.00043 ppm (Ae. taeniorhynchus and An. quadrimaculatus) to 0.023 ppm (Ae. albopictus). Chironomus crassicaudatus and G. paripes also were extremely susceptible (48-h LC50 of both species: 0.00042 ppm) to fipronil. Larval mortality checks of Ae. taeniorhynchus, Cx. nigripalpus, and G. paripes at 24 h and again at 48 h posttreatment revealed delayed activity of this compound against these species. First-instar larvae of Ae. albopictus and Cx. quinquefasciatus were significantly (P < 0.01) more susceptible to fipronil than the 4th-instar larvae of these mosquito species.