Since 2007 we have began to consider the relationships between the different members of the Bemisia tabaci species complex in a more structured and systematic way. Much of these relationships has been infered from considerations of a portion of the mitochondrial cytochrome oxidase one (mtCOI) gene. While this is a quite limited approach which would benefit from the consideration of a much greater diversity of genetic material, it is the only publically available data that spans the diversity of the species complex. Despite the limitations, the phylogenetic reconstruction that can be derived from this data is useful and can be used as a basis to frame questions and construct testable hypotheses that will form the basis for future research. This study uses the largest available mtCOI dataset, consisting of 383 unique mtCOI haplotypes that spans the full diversity of the B. tabaci species complex as we currently know it, to make a range of observations which are then used to develop questions as guide for future research.

The worldwide distribution and extensive genetic diversity of the whitefly, Bemisia tabaci, has long been recognized. However, the levels of separation within B. tabaci and the nomenclature of the various genetic groups have been a subject of debate. Recent phylogenetic analyses indicate that B. tabaci is a complex composed of 28 morphologically indistinguishable species. In this article, we first review the debate and difficulties associated with B. tabaci’s taxonomy and systematics, and argue for the need to apply the biological species concept in order to elucidate B. tabaci’s systematics. We summarize the accumulated genetic and behavioural data on reproductive incompatibilities evident amongst phylogenetic mtCOI groups of B. tabaci. Crossing studies have been conducted with 14 of the 28 putative species covering 54 reciprocal inter-species pairs, and observations on mating behaviour have been conducted for seven species pairs. Data from both crossing trials and behavioural observations indicate a consistent pattern of reproductive isolation among the putative species. We then discuss the technical and conceptual complexities associated with crossing experiments and behavioural observations designed to reveal reproductive incompatibility. Finally, we elaborate on a strategy for further clarifying the pattern of reproductive isolation between B. tabaci groups and propose future research directions on the systematics of this complex.