SCREENING OF HAEMATOBIA-IRRITANS IRRITANS (DIPTERA, MUSCIDAE) POPULATIONS FOR PYRETHROID RESISTANCE-ASSOCIATED SODIUM-CHANNEL GENE-MUTATIONS BY USING A POLYMERASE-CHAIN-REACTION ASSAY

A polymerase chain reaction (PCR)-based rapid screening procedure was developed to test individual horn flies, Haematobia irritans irritans (L.), for the presence of a specific nucleotide substitution in the so dium channel gene sequence that has been associated with pyrethroid re sistance. By a systematic optimization of reaction conditions and judi cious choice of FCR primers differing in DNA sequence by a single nucl eotide, we identified pyrethroid-susceptible or resistant sodium chann el alleles in individual flies. Laboratory and field populations were examined by both the PCR assay and conventional filter paper bioassays with the pyrethroid cyhalothrin to verify that populations containing greater proportions of individuals with the resistant sodium channel allele DNA sequence also had higher bioassay LC50 values. The PCR assa y far resistance alleles gave definitive information on the genotype o f an individual fly and detected the presence of heterozygous individu als that might serve as reservoirs of resistance genes in field popula tions.