Bemisia tabaci (Hemiptera: Aleyrodidae) is a globally distributed pest composed of at least 34 morphologically
indistinguishable cryptic species. At least seven species of endosymbiont have been found infecting some or all members of
the complex. The origin(s) of the associations between specific endosymbionts and their whitefly hosts is unknown.
Infection is normally vertical, but horizontal transmission does occur and is one way for new infections to be introduced into
individuals. The relationships between the different members of the cryptic species complex and the endosymbionts have
not been well explored. In this study, the phylogenies of different cryptic species of the host with those of their
endosymbionts were compared. Of particular interest was whether there was evidence for both coevolution and horizontal
transmission. Congruence was observed for the primary endosymbiont, Portiera aleyrodidarum, and partial incongruence in
the case of two secondary endosymbionts, Arsenophonus and Cardinium and incongruence for a third, Wolbachia. The
patterns observed for the primary endosymbiont supported cospeciation with the host while the patterns for the secondary
endosymbionts, and especially Wolbachia showed evidence of host shifts and extinctions through horizontal transmission
rather than cospeciation. Of particular note is the observation of several very recent host shift events in China between
exotic invader and indigenous members of the complex. These shifts were from indigenous members of the complex to the
invader as well as from the invader to indigenous relatives.