颈双缘姬蜂与菜蛾啮小蜂的种间竞争

Interspecific competition between Diadromus collaris and Oomyzus sokolowskii, two major parasitoids of Plutella xylostella

在室内 2 6℃下 ,以小菜蛾作寄主 ,研究了颈双缘姬蜂和菜蛾啮小蜂间的寄主资源竞争。结果表明 ,颈双缘姬蜂攻击于 2、4龄幼虫期已被菜蛾啮小蜂产卵寄生的小菜蛾蛹 ,将其产卵器插入 ,但不会将卵产在已被寄生的蛹中。产卵器停留在已被寄生蛹内的时间 ,明显短于未被寄生蛹内的时间。对已被寄生的寄主蛹的攻击频率又随寄主蛹体内啮小蜂年龄的增加而下降。颈双缘姬蜂产卵器的插入对小菜蛾蛹内菜蛾啮小蜂的存活率没有影响。当存在被啮小蜂寄生的小菜蛾蛹时 ,颈双缘姬蜂对小菜蛾蛹的寄生率下降 ,但不会影响颈双缘姬蜂后代的雌性比。两种蜂的合计寄生率 ,较只有一种蜂存在时要高。

Interspecific competition between two major parasitoids, Diadromus collaris and Oomyzus sokolowski, of the diamondback moth, Plutella xylostella, was studied in the laboratory at 26℃. D.collaris females attacked and inserted their ovipositor into diamondback moth pupae that had been parasitized by O.sokolowskii since early 2nd and 4th instars, but refrained from oviposition into the hosts. The duration of ovipositor insertion was shorter (3-5s) in previously parasitized pupae than in unparasitized pupae (5-8s). The frequency of D.collaris ovipositor insertions into both parasitized and unparasitized pupae was similar, but it was reduced with the increasing age of O.sokolowskii immatures developing inside the host pupae. Ovipositor insertion by D.collaris did not reduce the survival of O.sokolowskii immatures inside the host pupae. Compared with instances when only unparasitized pupae were provided, the parasitism rate by D.collaris was reduced significantly by the presence of host pupae already parasitized by O.sokolowskii, but the sex ratio of the progeny produced by D.collaris was unaffected, when parasitized and unparasitized pupae were provided concurrently. However, the combined rate of parasitism by the two parasitoids was higher compared to that by one of the parasitoid.