Field and laboratory evaluations of the repellent activity of pyrethroids and natural products against biting/nuisance flies and mosquitoes of vertebrate hosts

Field tests on horses treated with fly sprays were compared with untreated controls. All Diptera on the horses were counted the day before treatment, immediately before treatment on test day 0 and then at 1, 2, 3, 5 and 24-hours after treatment by two investigators. Horse & Rider and Marigold Fly Repellent Sprays were moderately effective (54.6 to 89.5%) in repelling nuisance flies from pastured horses. Flicks and UltraShield® Fly Repellent Sprays were very effective (88.3 to 99.0%) in repelling nuisance flies from pastured horses. After single application, the Icaridin 20% Spray formulation demonstrated excellent repellency of nuisance and biting flies on pastured horses in central California. The average percent fly repellency was 82.6 to 99.1% for the first 24-hours of the field evaluation of 20% Icaridin Spray. There was an average of 82.8 and 86.0% repellency at 4 and 6-hours post-treatment, respectively, increasing to 99.1% at 8-hours and 91.8% at 24-hours post-treatment. Laboratory bioassays using mice as a surrogate host were employed to determine the repellent activity of pyrethroid insecticides against yellow fever mosquitoes, Aedes aegypti. Technical compounds were diluted in ethanol at concentrations of 10.0, 1.0, 0.1 and 0.01% a.i. and applied to the mice directly. A series of observations were conducted to determine “repellency” of the pyrethroids to the vector arthropods. Permethrin and cypermethrin were consistently active as repellent insecticides possessing irritant or excito-repellent properties in addition to acute toxic effects in the mosquito bioassays.