Restriction Fragment Length Polymorphism Analysis of a Sodium-Channel Gene Locus in Susceptible and Knockdown-Resistant House Flies, Musca domestica

Abstract

Resistance to DDT and pyrethroid insecticides in the housefly (Musca domestica) often involves a common mechanism termed knockdown resistance (kdr). The voltage-sensitive sodium channel is generally regarded as the primary target for these insecticides, and has been implicated in nerve insensitivity to these compounds conferred by kdr alleles. Part of the sodium channel gene, designated Msc, previously cloned from the housefly, was used to identify restriction fragment length polymorphisms (RFLPs) at this locus in susceptible, kdr (resistant) and super-kdr (highly resistant) houseflies. These RFLPs showed tight linkage to resistance in controlled crosses, providing the first genetic evidence that kdr, and hence pyrethroid mode of action, is closely associated with the sodium channel. We report here that sodium channel RFLPs at the Msc locus show much diversity amongst susceptible insects, but are strongly conserved in pyrethroid resistant laboratory and field populations. This further implicates the sodium channel as the site of resistance and suggests a common origin for the kdr and super-kdr alleles.