Behavioral inhibition of the house fly (Diptera: Muscidae) when exposed to commercial equine fly repellents

House flies can have negative consequences on the welfare of horses and other equids. Fly repellents in the form of on-animal sprays, wipes, or spot-ons are the most commonly used fly control method for horses. Many products are available, but repellent efficacy and duration of effectiveness may influence repellent choice by horse owners. A better understanding of the efficacy of common fly repellent products will help guide repellent selection to reduce fly pressure on horses. To evaluate commercially available repellents, house fly behavioral inhibition after application of three products marketed as natural (Ecovet, Equiderma, and Outsmart) and four with synthetic pyrethroids as active ingredients (Bronco, Endure, UltraShield, and Optiforce) was compared at 100, 50, and 25% concentration and at 15, 30, 60, 240, 1,440, and 2,880 min. Time and product were significant at all tested concentrations. The natural products performed as well as or better than the synthetic products at all dilutions and times. Ecovet in particular retained over 75% inhibition of flies for >1 d at the 100 and 50% concentrations. Differences were seen among products with pyrethroids, suggesting that formulation differences significantly affect efficacy. Cost and application suggestions are discussed, and these results will aid horse owners in selecting fly repellents to meet their individual needs.