A pilot study on the isotopic characterization of feeding habits of Diptera in a tropical rain forest

Flies (Diptera) are among the most diverse groups of insects and are known to utilize various food resources, including plants, detritus, microbial tissues, and fresh and dead animal tissues. However, their feeding habits in the field remain poorly understood. We conducted a pilot study to apply stable nitrogen (N) and carbon (C) isotope techniques to examine the feeding habits of flies in a tropical rain forest in Sarawak, Malaysia. The fly samples comprised 13 families and >18 species. The results showed significant differences in nitrogen and carbon isotope ratios (δ¹⁵N and δ¹³C) among families and species within a family. The observed pattern is largely consistent with their known feeding habits; flies that use carcasses and carrion as diets (e.g., Sarcophagidae and Calliphoridae) have significantly higher δ¹⁵N values than those likely utilizing plant-based diets (e.g., Cecidomyiidae). There were significant differences in δ¹⁵N values among the six species of Calliphoridae, which is consistent with insect succession on carcasses. The differences in δ¹⁵N may be explained by the use of carrion at different stages of decomposition, because microbial decomposition can lead to the ¹⁵N enrichment. Tachinid flies had relatively low δ¹³C values, reflecting the use of lepidopterans as a host. This pilot study shows that the δ¹⁵N and δ¹³C values of flies provide insights into the diversity of feeding habits of fly communities, which could also serve as an indicator of resource availability in an entire ecosystem.