90 species of Euplectrus are treated: 55 newly described, all from Area de Conservación Guanacaste (ACG), and 35 previously described species, of which 20 occur in ACG. Three of the previously described species (E. brasiliensis Ashmead, E. hircinus (Say), E. ronnai (Brèthes)) have unknown status, owing to missing or severely damaged type material. The new species, all authored by C. Hansson, are: Euplectrus alejandrovalerioi, E. alexsmithi, E. alvarowillei, E. andybennetti, E. andydeansi, E. annettewalkerae, E. billbrowni, E. bobwhartoni, E. carlosarmientoi, E. carlrettenmeyeri, E. charlesmicheneri, E. charlesporteri, E. chrisdarlingi, E. chrisgrinteri, E. corriemoreauae, E. daveroubiki, E. davesmithi, E. davidwahli, E. dianariasae, E. donquickei, E. eowilsoni, E. garygibsoni, E. gavinbroadi, E. gerarddelvarei, E. henrytownesi, E. howelldalyi, E. hugokonsi, E. iangauldi, E. jacklonginoi, E. jesusugaldei, E. jimwhitfieldi, E. jjrodriguezae, E. johnheratyi, E. johnlasallei, E. johnnoyesi, E. josefernandezi, E. lubomirmasneri, E. markshawi, E. mikegatesi, E. mikeschauffi, E. mikesharkeyi, E. ninazitaniae, E. pammitchellae, E. paulhansoni, E. paulheberti, E. paulhurdi, E. philwardi, E. robbinthorpi, E. ronaldzunigai, E. roysnellingi, E. scottshawi, E. sondrawardae, E. sydneycameronae, E. victoriapookae, E. wonyoungchoi. The species are described or redescribed, and thoroughly and uniformly illustrated, and included in two identification keys, one for females and one for males. Lectotypes are designated for eight species: Euplectrus catocalae Howard (♂), E. junctus Gahan (♀), E. leucotrophis Howard (♂), E. marginatus Ashmead (♀), E. pachyscaphus Girault (♀), E. platyhypenae Howard (♂), E. semimarginatus Girault (♀), Heteroscapus ronnai Brèthes (♂). One synonym is established: Euplectrus walteri Schauff is a junior synonym of E. testaceipes (Cameron). Brief image notes and host records are provided on the natural history of the wasps as well as the details of their morphology. Hosts are known for 74 Euplectrus species.
