Multiple origins of pyrethroid resistance in sympatric biotypes of Bemisia tabaci (Hemiptera: Aleyrodidae).

The two most damaging biotypes of Bemisia tabaci, B and Q, are sympatric in the Mediterranean basin and show high resistance to pyrethroids synergized by organophosphates. Previous work showed that in the B biotype, this resistance is associated with the L925I mutation in the para-type voltage gated sodium channel. Here we identified two mutations in the para-type voltage gated sodium channel associated with resistance to pyrethroids synergized by organophosphates in the Q biotype: the L925I mutation that occurs in the B biotype, and substitution of threonine to valine, at position 929 (T929V). To determine if the L925I and T929V mutations have single or multiple origins, we sequenced the DNA regions flanking the mutations from 13 B and Q strains collected worldwide. The survey identified five resistant alleles and five susceptible alleles. In the resistant alleles, the nucleotide diversity was low within biotypes (0.001), but high between biotypes (0.033). Nucleotide diversity in susceptible alleles was high between the two biotypes (0.028). These observations are consistent with multiple independent origins of resistance. Although the B and Q biotypes coexist in several regions of the Mediterranean basin, divergence in their DNA sequences at the para-type voltage gated sodium channel locus suggests gene flow between these biotypes is low or nil.