关键词: 菜蛾, 半闭弯尾姬蜂, 菜蛾盘绒茧蜂, 寄生, 种间竞争

Abstract: Interspecific competition between two parasitoids, Cotesia plutellae (Kurdjumov)(Hymenoptera: Braconidae) and Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae), was investigated at 25℃ in the laboratory, by exposing 3rd instar larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) to both parasitoids together or either parasitoid alone, and by exposing the host larvae already parasitized by one parasitoid to the other. When host larvae were exposed to both parasitoids in one arena, initial parasitism rates of the host by each species were not reduced by the presence of the other species; and the final joint parasitism rate by the two species was not significantly higher than that by either parasitoid alone. Both parasitoids could lay eggs in to host larvae previously parasitized by the other species, leading to occurrence of multiparasitized hosts. When host larvae were parasitized first by D. semiclausum and then immediately exposed to C. plutellae, or parasitized first by C. plutellae and then immediately exposed to D. semiclausum, nearly all ensuing parasitoid adults from the multiparasitized host larvae were C. plutellae. When host larvae parasitized by C. plutellae≥2 days earlier were exposed to D. semiclausum, all ensuing parasitoids from the multiparasitized hosts were of C. plutellae. When host larvae parasitized by D. semiclausum≥2 days earlier were exposed to C. plutellae, most host larvae could not survive to prepupae and most of the ensuing parasitoid adults from the hosts that supported successful parasitism were D. semiclausum. Dissections of host larvae at various time intervals after initial parasitism by both parasitoids showed that development of both parasitoids in multiparasitized hosts were somewhat arrested, and that the first instar larvae of C. plutellae could initiate physical attack on larvae of D. semiclausum and remove the latter. These results suggest that C. plutellae have an obvious advantage over D. semiclausum in competition when both parasitoids develop in the same host.

Key words: Plutella xylostella, Diadegma semiclausum, Cotesia plutellae, parasitism, interspecific competition