ABSTRACT: 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 (Euplectrusbrasiliensis Ashmead, Euplectrushircinus (Say), Euplectrusronnai (Brèthes)) have unknown status, owing to missing or severely damaged type material. The new species, all authored by C. Hansson, are: Euplectrusalejandrovalerioi, Euplectrusalexsmithi, Euplectrusalvarowillei, Euplectrusandybennetti, Euplectrusandydeansi, Euplectrusannettewalkerae, Euplectrusbillbrowni, Euplectrusbobwhartoni, Euplectruscarlosarmientoi, Euplectruscarlrettenmeyeri, Euplectruscharlesmicheneri, Euplectruscharlesporteri, Euplectruschrisdarlingi, Euplectruschrisgrinteri, Euplectruscorriemoreauae, Euplectrusdaveroubiki, Euplectrusdavesmithi, Euplectrusdavidwahli, Euplectrusdianariasae, Euplectrusdonquickei, Euplectruseowilsoni, Euplectrusgarygibsoni, Euplectrusgavinbroadi, Euplectrusgerarddelvarei, Euplectrushenrytownesi, Euplectrushowelldalyi, Euplectrushugokonsi, Euplectrusiangauldi, Euplectrusjacklonginoi, Euplectrusjesusugaldei, Euplectrusjimwhitfieldi, Euplectrusjjrodriguezae, Euplectrusjohnheratyi, Euplectrusjohnlasallei, Euplectrusjohnnoyesi, Euplectrusjosefernandezi, Euplectruslubomirmasneri, Euplectrusmarkshawi, Euplectrusmikegatesi, Euplectrusmikeschauffi, Euplectrusmikesharkeyi, Euplectrusninazitaniae, Euplectruspammitchellae, Euplectruspaulhansoni, Euplectruspaulheberti, Euplectruspaulhurdi, Euplectrusphilwardi, Euplectrusrobbinthorpi, Euplectrusronaldzunigai, Euplectrusroysnellingi, Euplectrusscottshawi, Euplectrussondrawardae, Euplectrussydneycameronae, Euplectrusvictoriapookae, Euplectruswonyoungchoi. 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: Euplectruscatocalae Howard (?), Euplectrusjunctus Gahan (?), Euplectrusleucotrophis Howard (?), Euplectrusmarginatus Ashmead (?), Euplectruspachyscaphus Girault (?), Euplectrusplatyhypenae Howard (?), Euplectrussemimarginatus Girault (?), Heteroscapusronnai Brèthes (?). One synonym is established: Euplectruswalteri Schauff is a junior synonym of Euplectrustestaceipes (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.
