Kawakawa and the hungry little caterpillars: the kawakawa looper <i>Cleora scriptaria</i> causes unique plant responses in kawakawa <i>Macropiper excelsum</i> leaves

Kawakawa (<i>Macropiper excelsum</i>), is an endemic plant of Aotearoa New Zealand. Kawakawa holds cultural significance to Māori as a rākau rongoā (medicinal plant). Kawakawa is traditionally used internally to relieve gastrointestinal and genitourinary problems as well as topically to treat a range of skin conditions and may have anti-diabetic properties. The kawakawa looper/whangawhanga (<i>Cleora scriptaria</i>) creates characteristic holes in kawakawa leaves and traditional mātauranga Māori (Māori knowledge) has identified that leaves eaten by the caterpillars have greater healing properties. To substantiate this traditional knowledge, we used Rapid Evaporative Ionisation Mass Spectrometry (REIMS), a metabolomics fingerprinting technique that does not require sample preparation and is suitable for spatial analysis, to measure metabolite differences between leaves exposed to different caterpillars. Three species; brindled bell moth (<i>Epalxiphora axenana</i>), brown headed leafroller (<i>Ctenopseustis obliquana</i>), and kawakawa looper (<i>Cleora scriptaria</i>), were fed on kawakawa leaves. Leaves with and without caterpillar damage were harvested from plants, adhering to Māori principles (tikanga), and stored at -80°C. REIMS with a laser interface was used to generate metabolite fingerprints from caterpillar eaten and non-eaten sections from the same leaf and other non-eaten leaves from the same plant, and differences determined using multivariate modelling. There were substantial differences in the metabolomic fingerprint between eaten and non-eaten leaves of the same kawakawa plants, and of uneaten leaves from plants that had no insect herbivory. We found no difference between artificially hole punched leaves and non-eaten leaves, suggesting that metabolic variation in leaves is due to the interaction between caterpillars and leaves. Further, differences were observed between eaten leaves of the three caterpillar species emphasising the specificity of plant responses to herbivore feeding. Our results support the mātauranga that the caterpillar causes a change in plant chemical composition, potentially increasing the plant’s medicinal value.