Stable isotope analysis, which is widely used for studying trophic relationships of invertebrates, requires a correct estimation of trophic fractionation factors as well as the proper choice of reference tissues. Different organs and body parts of large insects may vary in the isotopic composition of carbon (δ¹³C) and nitrogen (δ¹⁵N), though detailed information is available for a limited set of species only. In the field-collected larvae and adults of Oryctes nasicornis (Scarabaeidae) and Uloma rufa (Tenebrionidae), the range of δ¹³C and δ¹⁵N values for different body parts and organs (muscles, legs, wings, elytra, fat body, gonads, etc.) was 4.8‰ and 2.4‰, respectively. We suggest that the muscle tissue or legs of large insects should be preferably selected for isotope analysis. The isotopic composition of nitrogen in beetles did not depend on the ontogenetic stage and was not affected by metamorphosis. In larvae and adults of Tribolium confusum (Tenebrionidae) reared in the laboratory culture, the trophic fractionation factors of carbon (Δ¹³C) and nitrogen (Δ¹⁵N) were within the expected values (from −1 to 1.5‰ and from 3 to 5‰, respectively), though depended on the diet. Changes in the δ¹³C values during ontogenesis reflected changes in the lipid content and were strongly correlated with the C/N ratio.

Soil food webs channel most of the energy in terrestrial ecosystems. Temperate and tropical forests host different soil invertebrate communities, but consequent differences in the structure and functioning of soil food webs between these major biomes remain unknown. Here, we calculate energy fluxes to explore generic patterns in biomass and energy distribution across micro-, meso- and macrofauna in forest ecosystems spanning from southern taiga to tropical rainforests. Tropical soil food webs have either larger (monsoon forest) or smaller (rainforest) animal biomass than temperate ones, but have consistently higher energy flux, higher share of large organisms (macrofauna) in total biomass and distinct energy distribution. Specifically, tropical soil food webs have proportionally higher predation rates than temperate soil food webs and rely more on plant consumption (living roots), but less on bacterial, fungal and litter consumption. Earthworms act as food-web engineers promoting detrital energy pathways (litter, soil and deadwood consumption) in mixed broadleaved forests overriding climate-associated differences among forests. Our study shows a major change in soil food web from “brown” temperate to “green” tropical functional state, explaining functional implications of soil invertebrate community turnover across biomes.