Apanteles marginiventris(Cresson) is a major parasite of green cloverworm,Plathypena scabra(F.) on soybean in Arkansas.A. marginiventrisprefers 1st and 2nd stageP. scabralarvae as ovipositional hosts. Mean developmental time from oviposition to larval emergence from the host is ca. 8 days at 30°C and 11 days at 25°C. Pupal development ofA. marginiventrisranges from 3–5 days at 30°C and 4–7 days at 25°C. Mean adult longevity in the absence of hosts is ca. 5.6 and 9 days at 30° and 25°C respectively. Usually only one parasite develops within a single host. Parasitism byA. marginiventrisoccurs primarily during daylight hours. The mean number ofP. seabralarvae parasitized by a female during her life span is ca. 82.