Repellent and insecticidal efficacy of a new combination of fipronil and permethrin against stable flies (Stomoxys calcitrans)

BACKGROUND: A laboratory study was conducted to assess the repellent and insecticidal efficacy of a new combination of fipronil and permethrin (Frontline Tri- Act®/Frontect® Merial) against Stomoxys calcitrans (stable flies). METHODS: Sixteen dogs were allocated to two treatment groups. Eight dogs were treated with a new topical spot-on formulation containing 6.76% w/v fipronil + 50.48% w/v permethrin on Day 0 and eight dogs served as untreated controls. Each dog was exposed to approximately 100 stable flies on Days 1, 7, 14, 21, 28 and 35. After a one-hour exposure period, live flies were carefully aspirated into a vial, anesthetized with CO(2) and crushed to determine feeding status (fed or unfed). Any dead flies remaining on the dog or in the cage were crushed to determine feeding status and counted as fed or unfed. Repellency was defined as the percent reduction in the number of fed flies in the treated group as compared to the untreated control group, and insecticidal efficacy was defined as the reduction in the number of live flies at the end of each exposure period in the treated group as compared to the control group. RESULTS: Percent repellency was ≥96.6% through Day 28, and 88.7% on Day 35. Percent insecticidal efficacy was ≥ 98.3% through Day 35. CONCLUSIONS: A single topical administration of a new combination of fipronil and permethrin provides protection (repellency and insecticidal efficacy) from S. calcitrans on dogs for at least 5 weeks.