Esterase profiles of diazinon-susceptible and -resistant horn flies (Diptera : Muscidae)

A field population of horn flies, Hematobia irritans irritans (L.), exhibit ing diazinon resistance in bioassays also displayed high overall esterase a ctivity and organophosphate-insensitive acetylcholinesterase in dot blot ac tivity assays. Native polyacrylamide gels yielded a complex qualitative and quantitative profile of esterases that varied considerably among individua l flies from 9 populations, with 28 different esterase bands identified. Th e results from topical diazinon application experiments and subsequent anal ysis indicate that a number of specific esterases may contribute to diazino n resistance in the hem fly.