noneEnter Intraspecific competition was examined when superparasitism occured in Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), a solitary larval endoparasitoid of Plutella xylostella (L.) (Lepidoptera: Plutellidae) at 25[degree]C in the laboratory. The third instars were exposed to wasps for initial oviposition by two female wasps in succession at different time intervals. When two eggs were laid into the same host larvae within 10 min, there was lethal symmetrical competition by physical combats with mandibles between two first-instar larvae about two days post parasitization first instars. In asymmetrical competition, when a host larva was parasitized in succession by two female wasps at intervals of 24, 48, and 72h, the older larvae at most cases (86.7%, 95.0%, and 96.9%, respectively) killed the newly hatched ones mainly through physical attacks with sharp mandibles or encapsulation or melanization of late-laid eggs. When the interval of two ovipositions was 96 and 120 h, the parasitized hosts could not be easily superparasitized, with supurparasitism rate declined to 69.4% and 60.7%, respectively, among the superparasitised hosts, the younger wasps mostly died due to host death. The results suggest that the endoparasitoid C. vestalis generally makes use of both physical combat and physiological suppression to eliminate competitors in intraspecific competition and that outcome of competition principally depends on the time interval between two ovipositions by conspecific wasps. email undeliverable lfz(at)163.com