Bionomic data usually hold the key for understanding the life history of the target insect species. Here, we provide morphological characteristics of different larval instars of Acanthoscelides macrophthalmus (Schaeffer), a leucaena bruchine beetle species that is a potential biocontrol agent for the notoriously invasive plant Leucaena leucocephala. The scanning electron micrographs of the head capsule, antenna, clypeolabrum, maxilla, labium, leg, spiracle, and anus of the larval stage of A. macrophthalmus also are provided for the first time for this species, with most of the traits reflecting the taxonomic placement of A. macrophthalmus in the genus Acanthoscelides. Successive instars are determined accurately by using a model of the distribution of the width of the larval head capsule. Therefore, the data generated from this study represent baseline information for further biological control programs involving A. macrophthalmus.