Although expression of foreign genes in a crop species has been target techniques for powerful protection against insect pests, classical breeding programs using varietal resistance of a crop are still being processed. It is, however, frequently difficult to find key products expressed from resistance-related genes in the variety, and those action mechanism. Here, an unterminated story about seed of a mungbean (Vigna radiata) variety with high resistance against the adzuki bean weevil and the bean bug is introduced. The two insects cannot survive on seeds of the variety, although they well develop on susceptible ones. Molecular markers linked to the resistance were selected through BAC library screening and near isogenic lines, and finally a bruchid resistance gene was suggested after map-based cloning approaches. Starvation and chemicals were suggested for a resistant mechanism and a related factor through feeding and behavior experiments, respectively. The seed flour was extracted with organic solvents, and isolated into several fractions on chromatography. Several peaks on HPLC in a fraction were related with the high mortality of the bean bug. A partial structure in an isolated chemical was observed before full identification.