Gelman Dale B, Gerling Dan, Blackburn Michael A
Insect Biocontrol Laboratory, USDA, ARS, PSI, Beltsville, MD 20705, USA.
J Insect Sci. 2005 Dec 31;5:46. doi: 10.1093/jis/5.1.46.
It has been reported that the aphelinid wasp Eertmocerus mundus parasitizes all four nymphal instars of the sweet potato whitefly, Bemisia tabaci (Biotype B), with 3rd instars being the preferred hosts. The parasitoid lays its egg on the leaf underneath the host nymph. First instars hatch and later penetrate the whitefly. Previous studies have shown that the initiation of parasitoid penetration induces the host to form a cellular capsule around the parasitoid. As described here, females never oviposited once the 4th instar whitefly nymph had initiated adult development. First instar E. mundus larvae were observed under 2nd, 3rd and 4th instar whitefly nymphs, however, penetration did not occur until the whitefly had reached the 4th instar. The non-penetrating E. mundus larva almost always induced permanent developmental arrest in its 4th instar whitefly host and also caused a reduction in whole body host ecdysteroid titers. Therefore, unless there is a peak in molting hormone titer in the area local to penetration, it appears that the induction of capsule formation is not due to an increase in ecdysteroid titer. As the capsule formed around the penetrating parasitoid, host epidermal cells multiplied and became cuboidal and columnar, and relatively thick layers of new cuticle were deposited within the developing capsule, particularly near its ventral opening. The newly formed host cuticle was thinner in the dorsal part of the capsule and appeared to be absent at its apex. These results provide new information regarding the timing and dynamics of parasitoid oviposition and egg hatch as related to larval penetration, parasitoid-induced changes in whitefly development, molting hormone titers and the process of capsule formation.
据报道，蚜小蜂科黄蜂恩蚜小蜂寄生于烟粉虱（生物型B）的所有四个若虫龄期，其中三龄若虫是其偏好的宿主。这种寄生蜂将卵产在宿主若虫下方的叶片上。一龄幼虫孵化后，随后穿透粉虱。先前的研究表明，寄生蜂开始穿透会诱导宿主在寄生蜂周围形成细胞包囊。如本文所述，一旦四龄粉虱若虫开始成虫发育，雌蜂就不再产卵。在二龄、三龄和四龄粉虱若虫下方观察到一龄恩蚜小蜂幼虫，然而，直到粉虱达到四龄，穿透才会发生。未穿透的恩蚜小蜂幼虫几乎总是导致其四龄粉虱宿主永久性发育停滞，还会使宿主全身蜕皮甾体滴度降低。因此，除非在穿透部位局部区域蜕皮激素滴度出现峰值，否则包囊形成的诱导似乎不是由于蜕皮甾体滴度的增加。随着围绕穿透寄生蜂形成包囊，宿主表皮细胞增殖并变成立方形和柱状，并且在发育中的包囊内沉积了相对较厚的新角质层，特别是在其腹侧开口附近。新形成的宿主角质层在包囊的背侧部分较薄，并且在其顶端似乎不存在。这些结果提供了关于寄生蜂产卵和卵孵化的时间及动态的新信息，这些信息与幼虫穿透、寄生蜂诱导的粉虱发育变化、蜕皮激素滴度以及包囊形成过程有关。
