The larva of swallowtail butterflies feeds exclusively on members of the plant family. Phytochemical constraints are thought to be one of the major determination of host recognition and host shift. Female butterflies lay eggs in response to specific chemical property contained in their host plants. They perceive a variety of polar compounds as oviposition stimulants through the tarsal chemosensilla of the foreleg by drumming upon the leaf surface.
In the last two decades, oviposition stimulants have been extensively identified for swallowtail butterfly species. Based on these facts we have promoted a study to identify genes that are expressed in female foreleg tarsi and function in various steps involved in chemoreception for host plant recognition. Through analysis of more than 20,000 EST from cDNA library prepared from female tarsi of Papilio xuthus, we have identified a seven transmembrane receptor (7TMR) expressed specifically in female tarsi. The sensitivity of sensilla were decreased by the gene knock-down using RNAi to the one of oviposition stimulants specifically. We beleve that we have achieved an identification of gustatory receptor involved in the oviposition behavior from the swallowtail butterfly.
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