ABSTRACT: Background:We describe 25 new species in the genus Telothyria van der Wulp, 1890 from Area de Conservación Guanacaste (ACG) in northwestern Costa Rica. All species herein described were reared from an ongoing inventory of wild-caught caterpillars spanning two families (Lepidoptera: Crambidae, and Tortricidae). Our study provides a concise description of each new species using morphology, life history, molecular data, and photographic documentation; a redescription of the genus, and its type species as well as a revised key to species of Telothyria occurring in the Mesoamerican region. We also suggest seven new synonymies resulting in 11 new combinations. New information:The following 25 new species of Telothyria are described: T. aidani sp. n., T. alexanderi sp. n., T. auranticrus sp. n., T. auriolus sp. n., T. bicuspidata sp. n., T. carolinacanoae sp. n., T. clavata sp. n., T. cristata sp. n., T. diniamartinezae sp. n., T. duniagarciae sp. n., T. duvalierbricenoi sp. n., T. eldaarayae sp. n., T. erythropyga sp. n., T. fimbriata sp. n., T. fulgida sp. n., T. gloriashihezarae sp. n., T. grisea sp. n., T. harryramirezi sp. n., T. incisa sp. n., T. manuelpereirai sp. n., T. obscura sp. n., T. omissa sp. n., T. osvaldoespinozai sp. n., T. peltata sp. n., and T. ricardocaleroi sp. n.The following are proposed by Fleming & Wood as new generic synonyms of Telothyria: Comatacta Coquillett Syn. n., Floradalia Thompson Syn. n., Ptilomyia Curran Syn. n., Ptilomyiopsis Townsend Syn. n., Ptilomyoides Curran Syn. n., Euptilomyia Syn. n., Eutelothyria Townsend Syn. n.The following new combinations are proposed as a result of the new synonymies: Telothyria bequaerti (Curran, 1925) Comb. n., Telothyria cruenta (Giglio-Tos, 1893) Comb. n., Telothyria frontalis (Townsend, 1939) Comb. n., Telothyria insularis (Curran, 1927) Comb. n., Telothyria itaquaquecetubae (Townsend, 1931) Comb. n., Telothyria major (Thompson, 1963) Comb. n., Telothyria micropalpus (Curran, 1925) Comb. n., Telothyria minor (Thompson, 1963) Comb. n., Telothyria nautlana (Townsend, 1908) Comb. n., Telothyria plumata (Curran, 1925) Comb. n., Telothyria trinitatis (Thompson, 1963) Comb. n., Telothyria variegata (Fabricius, 1805) Comb. n. Musca tricincta Fabricius is synonymized under Telothyria variegata Fabricius, Syn. n. Telothyria schineri Fleming & Wood nom. n. is proposed as a replacement name for Miltogramma brevipennis Schiner.Additionally we provide redescriptions of two previously named species: the type species Telothyria cupreiventris (van der Wulp) due to its being the type species, and Telothyria relicta (van der Wulp) due to its having been reared as an outcome of the inventory.