Larvae of most clearwing moths (Lepidoptera, Sesiidae) are endophagous borers of many angiosperms, including their fruits, stems, and roots. Their localized feeding may lead to swellings on those plant parts, but whether the structures produced should be considered true galls is still controversial. In this study we describe a peculiar sesiid moth, Neospheciacecidogena sp. nov. whose larvae induce unusual, external galls on Cayponiapilosa (Vell.) Cogn. (Cucurbitaceae) in the Atlantic Forest of southernmost Brazil. The adults, egg, larva, pupa and the gall are described and illustrated based on light and scanning electron microscopy. Galls are cylindrical and unilocular; they are induced individually on axillary buds of the C.pilosa stem. Unlike larvae of other sesiids, those of N.cecidogena sp. nov. lack abdominal pseudopodia, and show reduced stemata and chaetotaxy. Pupation occurs inside the gall, after having overwintered in the last larval instar. A maximum likelihood tree constructed based on mitochondrial DNA (COI) sequences showed that N.cecidogena sp. nov. is monophyletic and has an average distance of 13% to species of Melittia. The genera Neosphecia Le Cerf, 1916 stat. rev., Premelittia Le Cerf, 1916 stat rev., and Melittina Le Cerf, 1917 stat. rev. are restored from synonyms of Melittia Hübner, 1819 ["1816"].
Keywords: Cucurbitaceae; Melittina; Neosphecia cecidogena; Premelittia; Neotropical region; insect galls; sesiid moths; taxonomy.