斑痔悬茧蜂对甜菜夜蛾幼虫龄期的选择及其生长发育的研究

Host-stage selection for Spodoptera exigua larvae and the effect on developmental parameters of solitary endoparasitoid in Meteorus pulchricornis(Hymenoptera:Braconidae)

在室内采用非选择性和选择性试验，研究了斑痣悬茧蜂（Meteorus pulchricornis）对不同龄期甜菜夜蛾（Spodoptera exigua）幼虫的选择以及后代的生长发育表现。在非选择性试验中，斑痣悬茧蜂虽然寄生所有1-5龄幼虫，但寄生率不同，对2-4龄幼虫的寄生率（〉70％）显著高于对1龄（53％）和5龄（20％）幼虫的寄生；寄生不同龄期寄主幼虫的后代寄生蜂生长发育表现亦存在差异，寄生2-4龄寄主幼虫的寄生蜂结茧化蛹率（〉95％）和羽化率（〉90％）高于寄生1龄和5龄幼虫的，而发育历期短于寄生1龄和5龄幼虫的；但后代寄生蜂成虫的体型（用后足胫节长度表示）随寄主幼虫龄期增长而逐渐增大。由此表明，甜菜夜蛾2-4龄幼虫对斑痣悬茧蜂的生长发育适合度表现更有利。在成对选择试验中，当5龄幼虫不在供选寄主组合中时，斑痣悬茧蜂喜好龄期较大的寄主幼虫，即最喜好4龄幼虫，最不喜好1龄幼虫；在4龄与5龄幼虫之间倾向于选择4龄幼虫，这与非选择性试验得出的结论基本一致。

In order to understand oviposition strategy of the uniparental endoparasitoid Meteorus pulchricornis on host larvae of the beet armyworm Spodoptera exigua, non-choice and paired choice experiments were conducted in the laboratory. Parasitism on different instar larvae and development performance of the parasitoid offspring were observed. In the non-choice experiment, though all five instars of host larvae were susceptible to parasitization, the parasitism differed in that the 2-4 instals were significantly parasitized （ 〉70% ） than the first instar （53%） and the fifth instar （20%）. The development performance of offspring parasitoids was also different among host instars where parastization commenced. Parasitoid larvae pupated （ 〉 95 % ） after egression and adulls eclosed （ 〉 90% ）, derived from eggs oviposited in 2-4 instar hosts, more than those from eggs oviposited in the first and the fifth instar hosts. Larval development time of the parasitoid, measured from oviposition to adult eclosion, was shorter for the 2-4 instar hosts than the first and the fifth instar hosts where eggs were deposited. Body sizes of offspring parasitoids, represented by hind tibia length, increased with host instars where the parasitization commenced. Combined fitness returns for the parasitoid showed that the second through the fourth instar hosts were more suitable for its development. In the paired-choice experiment, M. pulchricornis preferred older hosts to the young but the inverse occurred when the fifth instar host was offered, which was consistent with the conclusion from the non-choice experiment.