Effect of Diet and Metamorphosis on the Stable Isotopes of Ectropis grisescens (Lepidoptera: Geometridae)

Rationale Light stable isotopes ( δ 13 C, δ 15 N, δ 2 H, and δ 18 O) of Ectropis grisescens (Lepidoptera: Geometridae), a destructive tea leaf‐eating pest, were measured at different developmental stages. Isotope values of larval instars, pupae, and adult moth body tissues were determined to understand fractionation patterns at different life stages and to evaluate dietary isotopic change from food to insect to excrement. Methods Young Ectropis grisescens larvae (collected before the first instar) were raised on Camellia sinensis tea leaves (Yingshuang cultivar) under controlled conditions at the Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, China. The two different tea leaf types were used to investigate trophic discrimination effects from consumer–diet responses and metamorphosis on Ectropis grisescens . Results Ectropis grisescens δ 13 C body tissue values were significantly more positive relative to its diet at different larval stages, whereas feces were generally more negative compared to dietary resources. Similarly, δ 15 N values of the body tissues at different larval stages were significantly more positive compared to its diet. This 15 N trophic discrimination was most likely due to available protein quality because both insufficient protein and a high dietary protein intake have the potential to enrich the 15 N of bulk body tissues through catabolysis or increased protein turnover. The δ 2 H and δ 18 O values of pest body tissues also showed significant differences compared to diet. A trophic‐related 2 H and 18 O decrease from early to late larval instars is seen, with an overall net decrease in δ 2 H and δ 18 O values from plant to the adult Ectropis grisescens . Conclusion Metamorphosis (pupae to moth) of Ectropis grisescens affected all stable isotopes, with δ 13 C, δ 15 N, and δ 2 H values increasing, whereas δ 18 O values showed a marked decrease from pupae to moth tissue.