Host-plant chemistry influences oviposition choice of the spicebush swallowtail butterfly

The spicebush swallowtail, Papilio troilus (L.), lays its eggs on plants in the family Lauraceae. Sassafras [Sassafras albidum (Nutt.) Nees], spicebush [Lindera benzoin (L.) Spreng.], redbay (Persea borbonia (L.)] and camphortree [Cinnamomum camphora (Nees) Eberm.] are four of its known host plants. in one-choice tests, free-flying spicebush swallowtail females laid eggs on chemical extracts of the leaves of each of these four hosts. In two-choice experiments, females always preferred to oviposit on an extract of sassafras compared to extracts of the other three hosts. It was shown for spicebush extract that this response was not due to oviposition experience. Previously we had identified one of the host plant chemicals acting as an oviposition stimulant in sassafras extract as 3-caffeoyl-muco-quinic acid (3-CmQA). Extracts of the other three hosts did nor contain this compound. The addition of 3-CmQA alone to spicebush extract did not increase oviposition activity. It did, however, increase discrimination between hosts and nonhosts. When a fraction of sassafras extract containing 3-CmQA and other synergistic stimulants was added to spicebush extract, preference for sassafras extract was no longer recorded. These results show existing differences in oviposition chemistry among host plants of the spicebush swallowtail and how these differences can influence oviposition choice in bioassay experiments.