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Lithosiini (Lepidoptera: Erebidae: Arctiinae) is distinctive in having some species that feed on lichens, whereas the majority of moths feed on vascular plants. However, the larval diet of most Lithosiini species is poorly known. This study examines whether Lithosiini species, collected in a tropical rainforest of Borneo (nine species) and a temperate forest of Japan (eight species), feed on lichens as larvae, based on stable isotope analyses. As a result, the δ¹⁵N values for eight of nine Lithosiini species collected from Borneo were notably lower than those of nine co-occurring herbivorous non-Lithosiini species, and were similar to those of sympatric, lichen-feeding termites; however, δ¹³C and δ¹⁵N values of one Lithosiini species (Adites sp.) were significantly higher than those of the other moth species and similar to those of humus-feeding termites and predatory insects occurring at the same site. These results have suggested that the Lithosiini in the Southeast Asian tropical rainforests contain some species that feed on lichens as their larval main diet and at least one species whose larvae feed on humus or animal-derived materials. In contrast, the δ¹³C and δ¹⁵N values of all examined Lithosiini species (eight species) in the temperate forest have suggested that their larvae fed on plants and not on lichens. Our stable isotope ratio analysis presented quantitative evidence suggesting lichen-feeding by Lithosiini moths in a tropical rainforest without observation of feeding behavior during the larval stages.

This study quantified the numbers and sex ratio of adult Sericania hidana (Coleoptera: Scarabaeidae) in a subalpine forest in 2017. Data from an area littered with coarse woody debris (CWD) created by a typhoon in 1959 were compared with those from an area where CWD had been cleared by salvage logging. Three types of traps were used: flight interception traps (FITs) with a black light, pitfall traps (PITs), and soil emergence traps (SETs). Carbon and nitrogen stable isotopes were analyzed to evaluate S. hidana diets and habitats. Overall, there were more S. hidana in the unsalvaged sites than in the salvaged sites. The FITs captured only males but SETs captured both males and females. The SETs on CWD captured more S. hidana than did SETs on soil in both the salvaged and unsalvaged sites. The PITs captured only a few individuals; thus, PITs are not suitable for studying this insect, although such traps were previously reported to capture S. hidana adults. Stable isotope analyses suggested that S. hidana feeds on a variety of plant materials, including living plants and CWD. These results suggest that CWD has long‐term effects on insect populations. Soil emergence traps provide an effective method to quantitatively evaluate insect ecology, and FITs can effectively screen for the existence of insects.

Insects are the most diverse organisms and often the most abundant animals in some ecosystems. Despite the importance of their functional roles and of the knowledge for conservation, the trophic ecology of many insect species is not fully understood. In this review, I present how stable carbon (C) and nitrogen (N) isotopes have been used to reveal the trophic ecology of insects over the last 30 years. The isotopic studies on insects have used differences in C isotope ratios between C3 and C4 plants, along vertical profiles of temperate and tropical forest stands, and between terrestrial and aquatic resources. These differences enable exploration of the relative importance of the food resources, as well as movement and dispersal of insects across habitats. The 13C-enrichment (approximately 3‰) caused by saprotrophic fungi can allow the estimation of the importance of fungi in insect diets. Stable N isotopes have revealed food resource partitioning across diverse insect species above and belowground. Detritivorous insects often show a large trophic enrichment in 13C (up to 3‰) and 15N (up to 10‰) relative to the food substrates, soil organic matter. These values are greater than those commonly used for estimation of trophic level. This enrichment likely reflects the prevalence of soil microbial processes, such as fungal development and humification, influencing the isotopic signatures of diets in detritivores. Isotope analysis can become an essential tool in the exploration of insect trophic ecology in terms of biogeochemical C and N cycles, including trophic interactions, plant physiological and soil microbial processes.