From host to host, and continent to continent: Two phoresy‐enabled <i>Guimaraesiella</i> hitchhiker louse species revealed by integrative taxonomy (Phthiraptera: Ischnocera)

The 'core Guimaraesiella' comprise a morphologically rather homogeneous group of avian chewing lice (Phthiraptera), most of which remain undescribed. Based on an integrative approach combining morphological characters and analyses of COI barcoding sequences, we here describe two new species within this group: Guimaraesiella impiger new species and Guimaraesiella stellana new species. Both species were collected from hippoboscid flies in Singapore, suggesting that they are capable of moving phoretically between hosts. In at least G. impiger, this was confirmed as louse specimens from another 30 host species that were found to be conspecific with the holotype of G. impiger in our mOTU analysis. This, together with limited morphological variability between species, highlights the need to combine genetic and morphological data when identifying 'core Guimaraesiella' species from southeast Asia. Moreover, both louse species appear to be able to cross vast geographical distances. Guimaraesiella impiger is known from across southeast Asia as well as in Malawi, despite none of the known hosts occurring in both Asia and Africa. Guimaraesiella stellana is known from two host species, one in Singapore and one in Australia, separated by several known biogeographical barriers, which seem to have limited the range of all known closely related species to the Australo-Papuan region; how G. stellana arrived in Singapore on a nonmigratory host is presently unknown. These cases highlight that comparisons with only locally occurring louse species may not be a valid identification method for this group. As both species described here are morphologically similar, identification of cryptic species of lice in this group within Guimaraesiella may need to rely on COI barcodes or other molecular markers.