Odor Coding in Insects

Most organisms rely on their olfactory system to detect and analyze olfactory cues in the environment, cues that are subsequently utilized in the context of behavior. Odorants are recognized by olfactory sensory neurons (OSNs), which are located in the olfactory epithelia of vertebrates or in the dendrites of olfactory sensory cells within the sensilla on the antennal surface of insects (Buck and Axel 1991; Carlson 2001; Chess et al. 1992; Vosshall et al. 2000). The OSNs express odorant receptors (ORs), which are related to seven transmembrane G-protein-coupled receptors (GPCR) and transduce odorant binding to cellular excitation (see also Chapter 7). The olfactory system of the genetic model organism, the fruit fly , has been the focus of numerous investigations. has two pairs of olfactory organs, the antennae and the maxillary palps. Each antenna contains about 1200 OSNs housed in a total of 410 olfactory sensilla covering the antenna, while the maxillary palp has about 120 OSNs and 60 olfactory sensilla (Laissue and Vosshall 2007). The sensilla are of three morphological types: basiconic sensilla, trichoid sensilla, and coeloconic sensilla (Venkatesh and Singh 1984). Across insects, there is a beautiful diversity of sensillar morphologies, including pore plate sensilla, campaniform sensilla, sensilla ampullacea, and more (Kleineidam and Tautz 1996; Steinbrecht 1996). In recent studies, the OR gene family of has been identified and shown to comprise 62 defned members (Table 2.1) (Clyne et al. 1999; Gao and Chess 1999; Vosshall et al. 1999). Several studies have been dedicated to characterize the molecular receptive ranges of identified ORs (Dobritsa et al. 2003; Hallem and Carlson 2006; Pelz et al. 2006).