Mosquitocidal Activity and Mode of Action of the Isoxazoline Fluralaner.

Mosquitoes, such as and , are important vectors of human diseases. Fluralaner, a recently introduced parasiticide, was evaluated as a mosquitocide in this study. On and fourth-instar larvae, fluralaner had 24-h LC (lethal concentration for 50% mortality) values of 1.8 ppb and 0.4 ppb, respectively. Following topical application to adult , fluralaner toxicity reached a plateau in about 3 days, with 1- and 3-day LD (lethal dose for 50% mortality) values of 1.3 ng/mg and 0.26 ng/mg, suggesting a slowly developing toxicity. Fipronil outperformed fluralaner by up to 100-fold in adult topical, glass contact, and feeding assays on . These data show that fluralaner does not have exceptional toxicity to mosquitoes in typical exposure paradigms. In electrophysiological recordings on larval central nervous system, the effectiveness of fluralaner for restoring nerve firing after gamma-aminobutyric acid (GABA) treatment, a measure of GABA antagonism, was similar in susceptible Oregon-R and cyclodiene-resistant -1675 strains, with EC (half maximal effective concentration) values of 0.34 µM and 0.29 µM. Although this finding suggests low cross resistance in the presence of , the moderate potency, low contact activity, and slow action of fluralaner argue against its use as an adult mosquitocide for vector control.