The lesser grain borer (Rhyzopertha dominica F.) and the rice weevil (Sitophilus oryzae L.) are stored grain pests that cause significant economic losses in grain storage. This study aimed to analyze the impact of the chemical composition of wheat and barley grain (e.g., protein, fatty acids and total antioxidant capacity) on the development of two species of storage pests and to determine the relationship between the analyzed variables. The study involved the evaluation of 10 wheat cultivars and 10 barley cultivars under laboratory conditions. The observations included assessing the beetles’ progeny abundance, dust mass produced after feeding, and grain mass loss. The chemical composition of the tested wheat and barley cultivars was also determined, and the influence of different chemical compositions on insect development was investigated. The results of the experiment revealed diversity of resistance among cultivars to pest feeding. Larger populations of the lesser grain borer were observed on barley grains, while rice weevil populations were higher on wheat. Cultivars with higher protein and fat content were more susceptible to pest attacks. A connection between the amount of dust, grain mass loss, and the type of pest was also identified, indicating differences in feeding mechanisms and selective food preferences of these insects. The grain chemistry of wheat cultivars, including the content of fatty acids and antioxidants, significantly influenced the progeny abundance of S. oryzae, suggesting the potential of these components as natural barriers against storage pests. This study provides valuable insights for developing breeding strategies to enhance the natural resistance of new grain cultivars to these pests, contributing to the reduction of pesticide use. Statistical analyses confirmed the significance of differences in grain composition in varied resistance to the studied pests. The conclusions drawn from this work may help establish new storage and breeding practices, promoting sustainable agriculture and protecting natural resources.