Use of an allele-specific polymerase chain reaction assay to genotype pyrethroid resistant strains of Boophilus microplus (Acari : Ixodidae)

A polymerase chain reaction-based assay was developed to detect the presenc e of a pyrethroid resistance-associated amino acid substitution in Boophilu s microplus (Canestrini). The assay uses a simple method for the extraction of genomic DNA from individual larvae and genotypes individuals for the pr esence of a Phe --> Ile amino acid substitution in the S6 transmembrane seg ment of domain III of the para-like sodium channel, clearly distinguishing heterozygotes from homozygotes. High frequencies for this amino acid substi tution were found in the Corrales and San Felipe strains, which have target site insensitivity mechanisms for pyrethroid resistance. The Caporal resis tant strain contained lower yet substantial numbers of amino acid-substitut ed alleles. Low amino acid substitution frequencies were found in the susce ptible reference Gonzales strain and the Coatzacoalcos strain, which has me tabolic esterase-mediated pyrethroid resistance. The amino acid substitutio n was not found in six other strains that were susceptible to pyrethroids.