Vitamin E is known as a fat-soluble antioxidant agent whose most common and bioactive form in the nature is alpha-tocopherol. This substance is active in the electron transport chainprocess, where it reduces the free radicals that contribute to aging. Effects of vitamin E have mostly been investigated in fat-containing diets. However, dietary protein might also interact with vitamin E. As excess protein isconverted into fat for long term storage, protein consumption couldinteract with the anti-aging effects of vitamin E in the body. In this study, alpha-tocopherol was added to a protein-containing juvenile diet to investigatehow this could influence juvenile development and adult life history traits. This experiment was done on the neriid fly Telostylinus angusticollis, which is highly plastic to variation inlarval diet. The juvenile viability, development and survival, as well as the adult secondary sexual traits, aging and longevity, were examined