RESUMEN
Fly control for any species is most effectively implemented in the immature stages when insects can be eliminated before emerging as adults capable of transmitting pathogens or becoming nuisance pests. Yet a limited number of insecticide classes are available for treating larval development sites for dipteran pest species. The most recently introduced class of insecticides in the United States (US) is the isoxazolines, including fluralaner. In the US, fluralaner is currently exclusively labeled for use against ectoparasites in companion animals. However, research has shown that it has a wider effective target range beyond ectoparasites and could be developed as an insecticide for vector control. Here we tested a novel, proprietary, yeast microencapsulated (YME) formulation of fluralaner against the larvae of three pest species: Musca domestica L. (Diptera: Muscidae), Aedes albopictus Skuse (Diptera: Culicidae), and Culicoides sonorensis Wirth and Jones (Diptera: Ceratopogonidae). These species all naturally consume microorganisms as larvae, including yeasts. Fluralaner was successfully microencapsulated in Saccharomyces cerevisiae yeast. YME fluralaner was reconstituted in water at concentrations of 0.00001-0.1 mg/mL (Aedes and Culicoides) or 1-50 mg/mL (Musca) for use in dose-response assays. For each species, the LC50 at 24 h was estimated using probit analyses. YME fluralaner was highly effective against all species tested (Ae. albopictus LC50 = 0.000077 mg/mL; C. sonorensis LC50 = 0.00067 mg/mL; M. domestica LC50 = 2.58 mg/mL). Additionally, laboratory assays were conducted to determine product reapplication rates using LC50 rates. Reapplication rates to maintain <50 % emergence were five weeks (Ae. albopictus) and greater than eight weeks (C. sonorensis). The results presented here indicate YME fluralaner is a promising candidate for controlling larval insects that naturally feed on detritus, thereby bypassing cuticular penetration barriers and safely delivering the active ingredient to the target species.
Asunto(s)
Composición de Medicamentos , Insecticidas , Isoxazoles , Larva , Animales , Isoxazoles/farmacología , Larva/efectos de los fármacos , Larva/crecimiento & desarrollo , Insecticidas/farmacología , Aedes/efectos de los fármacos , Aedes/crecimiento & desarrollo , Aedes/microbiología , Saccharomyces cerevisiae , Moscas Domésticas/microbiología , Moscas Domésticas/crecimiento & desarrollo , Moscas Domésticas/efectos de los fármacos , Control de Insectos/métodosRESUMEN
BACKGROUND: Culicoides biting midges (Diptera: Ceratopogonidae) are economically important blood-feeding pests closely associated with livestock production. They are the principal vectors of two hemorrhagic disease viruses affecting both wild and domestic ruminants within the US: bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV). BTV impacts the US agriculture sector through direct commodity loss and strict international livestock trade restrictions. Yet, despite posing a considerable threat to US livestock, Culicoides are understudied, and management strategies are lacking. Current control tools for Culicoides are limited to synthetic chemicals, predominantly pyrethroids. With limited products available for livestock producers, proper pesticide rotation is difficult. The present study investigates the efficacy of fluralaner, an isoxazoline insecticide, beyond its current labeled use as an ectoparasiticide in anticipation of adding a new class of pesticides into rotation for use against biting midges. METHODS: The efficacy of fluralaner was evaluated by conducting contact, topical, and oral toxicity bioassays on adult female Culicoides sonorensis. Contact toxicity was assessed by using a modified WHO cone assay, which simulates exposure through landing on an insecticide-treated surface. A modified WHO topical toxicity assay, in which fluralaner dilutions were administered to the lateral thorax, was used to assess topical toxicity. For evaluation of oral toxicity, females were offered a blood meal spiked with fluralaner in an artificial membrane feeding system to simulate a systemic insecticide. RESULTS: Contact exposure of fluralaner did not cause extensive or consistent mortality. Even the highest concentration tested (100 mg/ml) resulted in an average of only 24.3% mortality at 24 h, and mortality did not significantly differ between exposed and control midges at any concentration. One hundred percent mortality was consistently achieved at concentrations of 1 mg/ml when fluralaner was applied topically. The LC50 for topical exposure to fluralaner at 24 h was estimated to be 0.011 mg/ml. Oral exposure to fluralaner through ingestion of a spiked blood meal proved to be the most effective exposure method, significantly increasing mortality in a dose-dependent manner at 1 h post-exposure. The LC50 at 24 h following ingestion was 14.42 ng/ml. CONCLUSION: Our results suggest that fluralaner is a viable candidate for use as an insecticide against adult biting midges if exposed orally, such as in a systemic given to livestock. As withdrawal period requirements for meat animals present unique yet definitive challenges, pharmacokinetic studies of isoxazoline drugs need to be pursued and finalized for livestock before fluralaner may be used as a management strategy in this manner. Alternatively, livestock not raised for consumption, such as hair sheep, would directly benefit from administering oral fluralaner as a component of a BTV disease management program.