Descriptions, host plants, and biological notes are given for three species of Tenthredinidae from Costa Rica. Waldheimia saurauia Smith & Nishida, sp. nov. (Blennocampinae) feeds on Saurauia montana Seem. (Actinidiaceae). Leseha Smith, gen. nov. (Selandriinae), includes two species that feed on ferns: Leseha vespa Smith & Nishida, sp. nov., feeds on Phlebodium pseudoaureum (Cav.) Lellinger (Polypodiaceae) and L. carranzae Smith & Nishida, sp. nov., feeds on Elaphoglossum bellermannianum (Klozsch) T. Moore, and E. lingua (C. Presl) Brack. (Dryopteridaceae). Stromboceros cruralis Konow, 1899 from Peru, Dochmioglene cubitalis Malaise, 1954 from southern Brazil, Siobla joergenseni Schrottky, 1913 from northern Argentina, Selandria limbata Kirby 1882 from Brazil, and Strongylogaster strigatus Enderlein, 1920 from southern Brazil, are all transferred to Leseha (combs. nov.).