Phylogenetic relationship of Haematobia irritans candidate odorant receptors (OR) with those of Stomoxys calcitrans, Musca domestica, and Drosophila melanogaster. The H. irritans (Hirr) genes are labeled in black, while the S. calcitrans (Scal) and M. domestica (Mdom) genes are labeled in pink and teal, respectively. D. melanogaster (Dmel) genes are labeled in purple. Lineages that include apparent expansions in muscids relative to DmelOr67d and DmelOr1a are shaded in grey and teal, respectively. Individual Drosophila genes for which 1:1 horn fly candidate orthologues were identified are labeled on the edge to assist with finding them in the tree.