Mt COI sequence analysis for Bemisia tabaci (Genn.) has revealed numerous phylogeographical groupings. 'Biotypes' or variants are recognized that exhibit phenotypic variation but the concept of 'biotype' and factors underlying the evolution of such variants is poorly studied. Phylogeographically, New World (NW) haplotypes represent at least three distinct clades at <2-6% divergence, whereas, Old World B. tabaci comprise about seven or more clades, which diverge amongst themselves and with NW B. tabaci by approximately 8-14%. Whiteflies harbor prokaryotic symbionts, some of which provide nutritional needs, and others that may be nonessential or deleterious. Other than primary endosymbionts, little is known about the extent to which other prokaryotic symbionts are associated with B. tabaci, and/or whether they influence biotype formation and evolution. Examination of symbionts for B. tabaci from different plant hosts and geographical locations has revealed a diverse array of microflora. Phylogenetic analysis of eubacterial 16S rDNA sequences indicates that all B. tabaci examined thus far harbor a primary symbiont, however, symbiont 16S rDNA and whitefly mt COI phylogenies were not strictly concordant. Secondary symbionts, representing two Enterobacteriaceae clades were identified for 13 of 20 B. tabaci collections, indicating whiteflies harbor a divergent array of prokaryotic 'associates', including Wolbachia which were detected in at least 33% of the B. tabaci examined. Further, anecdotal evidence suggests that insecticide resistance, degree of polyphagy and fecundity, natural-enemy complexes, and possibly indirect effects associated with ingestion and transmission of circulative, non-replicative plant viral pathogens they vector may also influence fitness and ultimately, biotype evolution.
Keywords: whitefly
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