Pyrethroid Resistance in the Horn Fly., Haematobia irritans (L.) (Diptera: Muscidae)

Abstract

Haematobia irritans (L.) populations were sampled from different locations in Louisiana and assayed with two pyrethroids, fenvalerate and permethrin. At the LD₅₀, resistance to fenvalerate relative to an unexposed horn fly population was 36-, 32-, and 10-fold greater in the Red River, Rosepine, and Ben Hur populations, respectively. Resistance to permethrin at the LD₅₀, level was 24-, 27-, and 10-fold greater in the respective populations. Thus, these horn fly populations were resistant to both fenvalerate and permethrin. The inherent irritancy/repellency of the pyrethroids for horn flies suggest that behavior may be a contributing factor to the pyrethroid resistance in these insects.