2nd Place: An evaluation of contact and topical toxicity of fluralaner on culicoides biting midges

Fluralaner is an isoxazoline pesticide currently labeled for use against ectoparasites under the names Bravecto® and Exzolt®. Previous studies have shown that fluralaner does have activity against adult flies, including Aedes aegypti and Musca domestica. The effects of fluralaner against Culicoides biting midges are unknown. Culicoides transmit bluetongue virus, which affects domestic ruminants and livestock production, but control tools for these insects are lacking. Here, we evaluated mortality of adult Culicoides sonorensis after contact and topical exposure to fluralaner.

Efficacy of fluralaner against C. sonorensis was tested by conducting modified WHO contact and topical toxicity experiments. Technical grade fluralaner was formulated in acetone at 100, 10, 1, 0.1, and 0.01ug/mL. Using a modified WHO cone assay, contact toxicity was evaluated at 1h and 24h. As significant mortality was not observed, the assay was repeated using concentrations 10x higher (10, 1, 0.1, 0.01, 0.001mg/mL). Significant mortality was not observed in the contact toxicity assays, even at 10mg/mL. Susceptibility to topical exposures are currently being assessed by administering a 20nL dose of the insecticide to directly the thorax of adult female C. sonorensis and observing mortality at 1h and 24h.

In its currently approved formulations, fluralaner is marketed as a systemic feedthrough for companion animals and poultry. The compound is ingested by blood-feeding insects, resulting in mortality. For Culicoides, this may be a more effective route of exposure. Future work will assess C. sonorensis mortality after ingestion of fluralaner in a blood meal, in addition to contact and topical toxicity experiments.