Sequence analysis of the knockdown resistance-homologous region of the para-type sodium channel gene from pyrethroid-resistant Boophilus microplus (Acari : Ixodidae)

Using reverse transcription polymerase chain reaction and degenerate oligon ucleotide primers, a partial para-homologous sodium channel cDNA was obtain ed from the southern cattle tick, Boophilus microplus (Canestrini). The cDN A sequence encoded the region in which knockdown resistance (kdr)-type muta tions have been identified in numerous insect species. Comparison of deduce d amino acids from the cDNA sequence showed high similarity with sodium cha nnels from other species, particularly in highly conserved repeat domains o f the sodium channel. Analysis of the kdr-homologous region of the genomic DNA sequences from several susceptible and pyrethroid-resistant tick strain s did not detect mutations. The result suggests novel mutations in the sodi um channel gene or metabolic detoxification may be involved in the resistan ce to pyrethroids in this tick.