Larvae of Sasakia charonda (Lepidoptera: Nymphalidae: Apaturinae) and three related species use oral odorants to repel ants and wasps

We incidentally discovered that the larvae of Sasakia charonda (Hewitson, 1863) (Lepidoptera: Nymphalidae: Apaturinae) disturbed by ants, wasps, or humans release volatile compounds orally. To identify these substances, we collected oral odorant samples directly from the mouths of S. charonda larvae into volatile-collecting tubes. The trapped oral odorant samples were subjected to gas chromatography–mass spectrometry (GC–MS). We confirmed the identity of 19 substances by comparing them to GC results of known standards and inferred them to mainly be alcohols and aldehydes/ketones, with main chains of 4–5 carbons. Three of the chemicals in the oral odorant samples, 2-butanol, 1-penten-3-ol, and 3-pentanone, showed a repellant effect on the ants Pristomyrmex punctatus (Smith, 1860) and Formica japonica Motschoulsky, 1866 (Hymenoptera: Formicidae). We also examined the effects of these 19 volatiles on Polistes spp. (Hymenoptera: Vespidae) and confirmed that some of them were effective repellants against these wasps. We propose that the substances we identified in this study can be used as defensive chemicals, analogous to the osmeterium emissions specific to Papilionidae butterflies. Furthermore, we examined the oral odorants of three related Japanese Apaturine species, Hestina assimilis (Linnaeus, 1758), H. persimilis (Westwood, 1850), and Apatura metis (Freyer, 1829) using the same approach. The chemical compositions of the oral odorants of H. assimilis and H. persimilis were similar to that of S. charonda, whereas that of A. metis differed. Some of the oral substances also induced a defensive response in conspecific Apaturinae larvae. We consider these substances to also act as alarm pheromones in these larvae.