Discovery and phylogeny of the odorant binding and chemosensory proteins of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae) and Rhagoletis (Diptera: Tephritidae)

Although great strides have been made, we still lack a complete understanding of the molecular aspects of insect olfaction. Such knowledge has applications in pest control, as well as being crucial to understanding specific olfactory pathways and their evolution. Evidence suggests that both odorant-binding proteins (OBPs) and neuronal receptor proteins play roles in odorant recognition. One hypothesized function of chemosensory proteins (CSPs) and OBPs is to bind and transport specific odorants to olfactory receptors, thereby acting as selective filters. The purpose of this study was to recover and characterize putative olfactory proteins from the agricultural pests, Diabrotica virgifera and Rhagoletis suavis. OBPs and CSPs were recovered using an expressed sequence tag approach. Their protein structures were characterized, and their intraspecific relationships and phylogenetic positions within the insect OBP and CSP gene families were estimated. Thirteen OBPs and three CSPs were recovered from D. virgifera. These are the first CSPs to be reported from beetles. Nine of the D. virgifera OBPs have only four of the six cysteines usually conserved in members of the OBP gene family. Apparent D. virgifera OBP and CSP homologues were not identified from other insects, except that OBP 1 is a putative orthologue of scarab pheromone-binding proteins. Nine OBPs and two CSPs were recovered from R. suavis; all are putative orthologues of Drosophila melanogaster proteins. Two R. suavis OBPs, KAR and SAR, were used to investigate the phylogeny of the R. pomonella sibling species complex. Early divergence by R. cornivora and a distinct R. zephyria lineage were found in most estimates. Relationships of the close pomonella species, R. pomonella, R. mendax and the flowering dogwood fly, were unresolved. A separate lineage for flies from the Mexican highlands found weak support one analysis. A SAR DNA analysis highly supported a clade of flies from mayhaw hosts. This is the first study to find that mayhaw flies are distinct from southern R. pomonella. The mature SAR proteins of the R. pomonella species complex are invariant, which might be due to a high level of stabilizing selection, whereas the mature KAR proteins have variations that suggest diversifying selection.