none Adult and immature stages of Prosetomorpha falcata, a new genus and species of tineid moth from Colombia, are described and illustrated. Prosetomorpha is remarkable in being the most plesiomorphic setomorphine tineid discovered, as evidenced by the five-segmented maxillary palpi, moderately well developed haustellum, mandibles vestigial but distinct, female with signum present, and larva with six pairs of stemmata. Synapomorphies shared with other Setomorphinae include similar semi-appressed head vestiture, annulate but completely fused, eighth abdominal tergosternum in the male, membranous eighth abdominal segment without rami in the female, and larvae with unidentate mandibles. The larva is believed to be primarily a scavenger within the burrows of a curculionid weevil, Faustinus apicalis (Faust), that bores in the stems of Solanum quitoensis var. quitoensis Lamarck and S. quitoensis var. septentrionale R. E. Schultes. A braconid parasitoid, Promicrogaster sp., has been reared from burrows occupied by Prosetomorpha.