The swallowtail butterfly, Papilio xuthus, only feeds on select members of the citrus family. How does the female butterfly discriminate host from non-host plants? Swallowtail butterflies use chemotaxonomy, the chemicals present in a plant. The Xuthus Swallowtail “identifies” its host plant by a mixture of 10 chemicals present in the plant leaves.
Like most insects the “taste” receptors that identify the plant chemicals are on its legs. The legs are a much more convenient location for taste receptors than the mouth, because the butterfly can get information about a plant as soon as it lands. As it walks from plant to plant, it “tastes” the plant chemicals. If taste receptors were confined to the mouth, lowering the mouthparts to taste every plant would be much less convenient.
Human taste receptors are typically classified as “salt” “sweet”, “sour” and “bitter”. In the Swallowtail, some of the “taste” receptors are more specific than generic “bitter”. These receptors respond preferentially to one or only a few chemicals that are associated with the butterfly host plant. The genes and receptors of Swallowtails are under study*. These studies may lead to improvements in biosensors that can detect important chemicals in our environment.
*Gustatory Sensing Mechanism Coding for Multiple Oviposition Stimulants in the Swallowtail Butterfly, Papilio Xuthus. Masasuke Ryuda, Delphine Calas-List, Ayumi Yamada, Fre ́de ́ric Marion-Poll, Hiroshi Yoshikawa, Teiichi Tanimura, and Katsuhisa Ozaki. J. Neurosci., January 16, 2013 • 33(3):914 –924