We report the first record of occurrence of Loncophorus longinasus in fruits of munguba, Pseudobombax munguba, in the state of Amazonas, Brazil. Some morphological and biological aspects of L. longinasus are presented. Adults were obtained through natural emergence from munguba fruits that opened for seed dispersal. The fruits had perforations leading to galleries through the exocarp. Inside the fruit, larvae were found at the seed insertion points on the central seed attachment structure. The pupae developed in a cocoon at the same structure and turned mature simultaneously with the capsule opening. Together with the larvae, the presence of ants (Pseudomyrmex sp.) was observed, that apparently maintained the galleries open for access and feeding on larval exudates. (AU)