Animal uses its olfaction and gestation systems for host selection, courtship and escaping predators in heterogeneous chemical environments.Several families of proteins, odorant receptor (Or), odorant-binding protein (OBP) and chemosensory protein (CSP) have been shown to participate in these two systems.Most Ors have been identified in the holometabolous insect, particularly model Drosophila, and some of them have been functionally studied.