Acanthoscelides obtectus (Say, 1831) (Coleoptera: Chrysomelidae: Bruchinae) is a beetle with a cosmopolitan distribution that causes severe damages to diverse species of the Fabaceae family. This work is the first report of its infestation on Senna multiglandulosa (Jacq.) H.S. Irwin & Barneby, 1982 (Fabaceae) bushes in the central Andean region of Peru. The morphology of the biological stages of A. obtectus and the perforations made on infested legumes collected in three sites of the Mantaro Valley from January to December 2018 are described. The total length (L) and width (W) of eggs, larvae, pupae, and adults of A. obtectus and the diameter (D) of the perforations on pods and seeds of S. multiglandulosa were measured. The results showed significant differences in the size of each stage (p < 0.001), and their perforations on legumes (p < 0.001) affect mainly the seeds of S. multiglandulosa, becoming a severe health problem for the studied plant.