Sequence and transcript expression of the super‐kdr locus of the horn fly, Haematobia irritans

In horn flies, Haematobia irritans irritans (Diptera: Muscidae) (Linnaeus, 1758), target site resistance to pyrethroids can be diagnosed by an allele‐specific PCR that genotypes individual flies at both the super‐kdr (skdr) and the knock down resistance (kdr) associated loci. When this technique uses genomic DNA as template, modifications, such as alternative RNA splicing and RNA editing are not specifically detected. Alternative splicing at the skdr locus has been reported in Dipterans; thus, the genomic DNA‐based allele‐specific PCR may not accurately reflect the frequency of the skdr mutation in horn fly field populations. To investigate if alternative splicing occurs at the skdr locus of horn flies, genomic DNA and cDNA sequences isolated from two wild populations and two laboratory‐reared colonies with varying degrees of pyrethroid resistance were compared. There was no indication of alternative splicing at the super‐kdr locus neither in the wild populations nor in the laboratory‐reared colonies. All cDNA clones had the same nucleotide sequence, differing only at the super‐kdr locus. The cDNA and genomic sequences were identical matches, except for a variable intron in the genomic sequences. Unlike what has been reported for other Dipterans, only exon d of the sodium channel was found in the studied horn fly populations. There was no indication of alternative splicing at the super‐kdr locus, neither in the wild populations nor in the laboratory‐reared colonies.