Callosobruchus maculatus females attach their eggs individually to the seed coat. Oviposition is completed in about 8 days, eclosion occurs within the seed, and the adult beetles emerge some 25-30 days after oviposition. Before the larva reaches the cotyledons, where it will complete its life cycle, it is necessary that it crosses the seed coat, which represents a critical event because of the physical characteristics and toxicity of this tissue. In this work we studied the influences of the seed coat in the capacity of larvae to penetrate the seeds and the toxicity of the natural seed coat from four cultivated and twelve native legume species over Callosobruchus maculatus larval development. The toxicity was studied by using an artificial seed system, where artificial seeds were covered with natural seed coats and through the incorporation, in those artificial diets, of seed coat flours, in concentrations that varied from 0.1 to 16.0 %. After 20 days, the toxicity was evaluated by determining the larval weight and rates of larval survival compared with control larvae. Experiments with natural seeds, infested by C. maculatus, showed that almost no insect was capable of penetrating the seed coat and of emerging up to 40 days after the oviposition. All seed coats tested were toxic to insect larvae. They have considerably reduced the survival and weight of larvae and the levels of toxicity varied from species to species. Tephrosia adunca seed coat showed the highest toxicity, with values of WD₅₀ (lethal dose that reduced larvae weight to 50 %) of 0.12 % and LD₅₀ (lethal dose that reduced the number of surviving larvae to 50 %) of 0.15 %. The toxicity levels were not well correlated to the state of being cultivated or native species. In the experiments with the artificial seed system covered with natural seed coat, we observed that no eggs laid on Albizia sp. and Dioclea altissima seed coats have ecloded. The number of dead larvae on the Canavalia ensiformis seed coat was about 75 %. In these experiments we observed that about 93 % of larvae laid on Glycine max coat survived after 20 days, however the larvae developed in these experiments had only 50 % of the mass of a normal larva. This results show that the expression of C. maculatus detrimental compounds in the seed coats of non-host seeds may have been important for the evolutionary discrimination of legume seeds by this bruchid. Supported by FAPERJ, UENF and CNPq.