Whiteflies belonging to the Bemisia tabaci species complex can be highly damaging pests to a wide range of field and greenhouse crops worldwide. Strategies to manage this pest complex, however, are complicated by the biological diversity that exists in this group of morphologically-cryptic, putative species. The systematic framework relies currently on a partial sequence of the mitochondrial cytochrome oxidase I gene (mtCOI) and a set of crossing experiments showing the reproductive isolation among some of the >34 putative species. A threshold of 3.5% pairwise sequence divergence of the partial mtCOI has been proposed as a method for grouping populations into species.
In our study, we investigated the species status of the highly devastating ‘Mediterranean’ (MED) genetic group, currently recognised as having four intra-species subclades, called Q1, Q2, Q3 and ASL. Of these, MED-Q1 and MED-Q2 have spread invasively outside their indigenous regions and are often resistant to a range of insecticides.
We performed (i) reciprocal crossing experiments to investigate reproductive compatibility among three MED subclades, (ii) molecular screening for bacterial endosymbionts, (iii) genome sequencing from single males, and (iv) bioassays to assess their host-plant range and performance.
Our results showed reproductive incompatibility and differences in host-plant performance within MED. These data will be presented in the context of how differences in endosymbiont content may influence biology and reproductive compatibility. The utility of next-generation genome sequencing in analysing the metagenome and identifying pseudogenes will also be discussed.
Our study reviews the method of species delimitation currently applied to the B. tabaci complex and explores the way forward in resolving systematics of cryptic species complexes. Knowledge about the number and biology of cryptic species will allow more targeted and efficient design of pest control strategies.