A new species of Periergates Lacordaire, 1872 (Coleoptera: Cerambycidae: Lamiinae: Onciderini) from Costa Rica is described: Periergates kenjii Nearns & Swift, sp. nov. All life stages (egg, larva, pupa, and adult) are described and illustrated. Girdling behavior in Periergates is reported for the first time. Eight host plants are recorded for the new species: Cojoba costaricensis Britton & Rose (Fabaceae), Quercus cortesii Liebm. (Fagaceae), Q. insignis M. Martens & Galeotti, Alfaroa williamsii Ant. Molina (Juglandaceae), Cinnamomum tonduzii (Mez) Kosterm. (Lauraceae), Persea sp. (Lauraceae), Psidium guajava L. (Myrtaceae), and Ardisia costaricensis Lundell (Primulaceae). Periergates chiriquensis Bates, 1885 is excluded from the Costa Rica fauna, and a key to the known species of Periergates is provided.