Increased Susceptibility of Pyrethroid-Resistant Horn Flies (Diptera: Muscidae) to Chlorfenapyr

Abstract

Chlorfenapyr (AC 303630) was found to be 5 times as toxic to pyrethroid-resistant horn flies, Haematobia irritans (L.), as to susceptibles. We hypothesize this difference occurs because higher levels of mixed function oxidases in the resistant flies convert more chlorfenapyr (a proinsecticide) to the insecticidal form. This negative cross-resistance between chlorfenapyr and pyrethroids offers new resistance management possibilities.