Stable isotope ratios of nitrogen (δ¹⁵N) and carbon (δ¹³C) have become useful tools for assessing the feeding ecology of organisms and the trophic structure of food webs. However, environmental variables such as temperature in addition to several variables associated with the organism (i.e. tissue sampled, amino acid composition, quality of food consumed) have been shown to influence stable isotope ratios in reference to diet-tissue fractionation. An additional variable which has not been investigated is developmental stage, which could be important for organisms that feed on multiple stages (i.e. larva, pupa, adult) of holometabolous aquatic insects. In this study, the stable isotope ratios of δ¹⁵N and δ¹³C and diet-tissue fractionation of δ¹⁵N and δ¹³C were investigated over the course of development of the black fly, Simulium vittatum IS-7, at various temperatures in a controlled laboratory setting. Initial results indicate that black fly larvae reared at lower temperatures have lower δ¹⁵N signatures resulting in temperature-specific diet-tissue fractionation factors. However, black fly pupae showed no difference in δ¹⁵N signatures at the various rearing temperatures. Additional data with adult black flies are forthcoming.