INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Relationship Between the para-Homologous Sodium Channel Point Mutation (g3 c at Nucleotide 2979) and Knockdown Resistance in the German Cockroach Using Multiplex Polymerase Chain Reaction to Discern Genotype

Extensive use of pyrethroid insecticides for urban pest control has led to widespread pyrethroid resistance in the German cockroach. A mutation at nucleotide position 2979 (G to C, causing a leucine to phenylalanine change) in the S6 transmembrane segment of domain II of the para-homologous voltage-gated sodium channel has been previously identiÞed in knockdown-resistant cockroaches and demonstrated by site-directed mutagenesis to reduce channel sensitivity to pyrethroids. In a recent survey, 83% of pyrethroid-resistant German cockroach populations were found topossess thismutation.AGermancockroach strainwith a low incidenceof theL993Fmutation was subjected to selection pressure with cypermethrin and subsequently evaluated over several generations for the knockdown resistance phenotype. Correspondingly, we determined the genotype of individual cockroaches of each population at the 2979 position of the para-homologous gene. Genotype was discerned by development of a polymerase chain reaction method that employed a mismatched primer-template set. A direct relationship was observed betweenmean knockdown time and the presence of the kdr mutation. Furthermore, individuals homozygous for the kdr mutation exhibited a signiÞcantly higher mean knockdown time than heterozygotes or wildtype cockroaches. This is the Þrst report demonstrating the progressive expression of the kdr allele in response to insecticide selection pressure.