Chemosensory-Related Gene Family Members of the Horn Fly, Haematobia irritans irritans (Diptera: Muscidae), Identified by Transcriptome Analysis

Simple Summary Horn flies are blood-feeding ecoparasites that have a significant economic impact on cattle producers in the United States and worldwide. Insecticides have been utilized to reduce horn fly populations, but the development of insecticide resistance has prompted evaluation of alternative control approaches. Compounds isolated from natural products have shown some success in modifying interactions between the horn fly and its host. A more thorough understanding of the horn fly chemosensory pathway would enable identification of species-specific compounds. We assembled a database of genes that are expressed in appendages on the fly head that have a role in sensory input and compared these with genes expressed in adult fly bodies from which heads were removed. We identified genes that were enriched in head appendages and these were similar to previously described genes known to mediate an insect's response to a chemical stimulus. These included odorant binding proteins and chemosensory binding proteins, as well as receptors that have a role in facilitating responses to odor and/or taste compounds, namely odorant, gustatory, and ionotropic receptors. These findings provide a resource to enable future studies targeting horn fly chemosensation as part of an integrated strategy to control this blood-feeding pest. Horn flies are one of the most significant economic pests of cattle in the United States and worldwide. Chemical control methods have been routinely utilized to reduce populations of this pest, but the steady development of insecticide resistance has prompted evaluation of alternative control strategies. Behavior modifying compounds from natural products have shown some success in impacting horn fly populations, and a more thorough understanding of the horn fly chemosensory system would enable improvements in the development of species-specific compounds. Using an RNA-seq approach, we assembled a transcriptome representing genes expressed in adult female and male horn fly head appendages (antennae, maxillary palps, and proboscides) and adult fly bodies from which heads were removed. Differential gene expression analysis identified chemosensory gene family members that were enriched in head appendage tissues compared with headless bodies. Candidate members included 43 odorant binding proteins (OBP) and 5 chemosensory binding proteins (CSP), as well as 44 odorant receptors (OR), 27 gustatory receptors (GR), and 34 ionotropic receptors (IR). Se