小菜蛾内寄生蜂--菜蛾盘绒茧蜂的种内竞争

在室内（25±1）℃，以小菜蛾3龄幼虫为初始寄主，对过寄生后，小菜蛾幼虫内寄生蜂--菜蛾盘绒茧蜂的种内竞争进行了研究。当2头雌蜂同时寄生（10 min内）同一头寄主，2 d后几乎同时孵化的茧蜂幼虫总有一头1龄幼虫利用发达的角质化上颚攻击同类竞争者。当两次寄生间隔时间为24、48和72 h时，先寄生的茧蜂幼虫分别以86.7%，95.0%和96.9%的比例在发育中占据优势，1龄幼虫使用上颚将后孵化的初孵幼虫杀死，或直接攻击蜂卵致使包囊、黑化的发生，此时物理攻击发挥主要作用，并可能通过先寄生者释放畸形细胞、水解酶等生理抑制方式完全阻碍后产入的蜂卵的发育。当两次寄生间隔时间长达96或120 h，因寄主已不适合茧蜂的再次产卵寄生，致使过寄生率由100%分别下降为69.4%和60.7%；已发生过寄生的个体中，80.0%以上以先寄生者吐丝、结茧化蛹，后寄生者则伴随被过寄生寄主的死亡而不能完成发育。以上结果表明，当种内竞争发生时，菜蛾盘绒茧蜂可通过物理攻击和生理抑制两种途径排除同类竞争者，竞争结果主要取决于雌蜂2次寄生的先后顺序。

Intraspecific Competition in Cotesia vestalis,a Solitary Endoparasitoid of Plutella xylostella Larvae

Intraspecific competition was examined when superparasitism occurred in Cotesia vestalis （Haliday） （Hymenoptera：Braconidae）, a solitary larval endoparasitoid of Plutella xylostella （L.） （Lepidoptera：Plutellidae） at 25℃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 72 h, 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 or 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.