Abstract <p>Trophic fractionation or trophic discrimination factor, is a key parameter in the stable isotope-based studies in trophic ecology. In this study, we investigated nitrogen (Δ¹⁵N) and carbon (Δ¹³C) trophic fractionation (TF) in larvae of multiple species of leaf beetles (Coleoptera: Chrysomelidae) – a group of herbivorous arthropods that share similar trophic habits. Despite this ecological similarity, Δ¹⁵N values across species ranged from 0.9 to 6.8‰, and Δ¹³C values from –0.2 to 3.0‰, with even greater variation observed at the individual level. The Δ¹³C values showed no significant correlation with the dietary C : N ratio, while Δ¹⁵N values were positively associated with the dietary C : N ratio; however, the proportion of explained variance was very low. The apparent dependence of TF on the isotopic composition of the diet (δ_diet values) was largely attributable to a spurious statistical association rather than a true biological mechanism. Our findings reveal substantial and unpredictable variability in TF even within a single insect family. While the mean Δ¹⁵N and Δ¹³C values were consistent with previously reported estimates, the extent of both inter- and intraspecific variation presents a major challenge for using TF as a precise tool for reconstructing trophic relationships. Field ecologists should acknowledge the variable nature of TF, which limits the precision of stable isotope-based trophic reconstructions.</p>