Insect diets are complex and usually contain antinutritional factors; because of this, modification of the digestive process and strategies to cope with the factors determines adaptation of each species. Pterophylla beltrani Bolivar & Bolivar is a forest pest that has two feeding regimes; P. beltrani feeds first on diverse vegetation but changes during the second regime to consume foliage of oaks (Quercus spp.). The goal of this work was to assess the status of digestive proteinases and phenolic-antioxidants in the two feeding regimes, as indicators of changes related to diet variation. Trypsin-like activity was confirmed by hydrolysis of a synthetic chromogenic substrate. Units of proteolytic activity were 25.2 to 46.1 for the first regime and 22.6 to 40.2 for the second. No differences in proteolytic profiles were detected between regimes. Total phenolic content was 1,152.2 and 759 GAE/ml for the first regime and 832.2 and 552.2 GAE/ml for the second when samples were extracted in water or ethanol, respectively. Differences in the antioxidant capacity also were observed in individuals from the different feeding regimes — large amounts of phenolics for the first regime and greater antioxidant capacity for the second. Diet allows differential accumulation of antioxidants that might be associated with physiological and ecological implications yet to be discovered.