Drosophila Gr5a: expression pattern, ligand profi le and transduction pathway
For those interested in studying insect chemoreception, Drosophila offers a fascinating feeding behaviour. Under natural conditions, fruit fl ies are most often encountered in the vicinity of overripe or rotten fruit, being attracted by the volatiles released as by-products of fermentation. These chemicals are detected by the olfactory organs located primarily on the distal segments of the antennae but also on the maxillary palps, a secondary olfactory organ of Drosophila. In contrast to the larvae, which are virtually surrounded by their food, the adults display a highly stereotyped feeding behaviour mediated by specialised taste organs associated with the distal parts of legs
(tarsi) and the mouthparts. Upon encountering potential food the adult fl ies initially evaluate food by literally stepping into it (Figure 1, top panel) and allowing any tastants present in it to make contact with the tarsal taste receptors. If these receptors are stimulated by potential nutrients, fl ies perform further evaluation by extending their proboscis (Figure 1, bottom panel), a structure formed by fused mouthparts (labella) and containing the central food canal. Once the food is determined to be acceptable, the extended proboscis is used for sponging the semi-liquid diet and pumping it into the gut. The quality of ingested food is further monitored by contact chemosensory structures in the pharynx.