Jones D, Gelman D, Loeb M
Graduate Center for Toxicology, University of Kentucky, Lexington 40506.
Arch Insect Biochem Physiol. 1992;21(2):155-65. doi: 10.1002/arch.940210208.
Regulation of ecdysteroid production in lepidopteran prepupae was studied using a parasitic wasp (C. near curvimaculatus) which specifically suppresses host prepupal ecdysteroid production after the induction of precocious host metamorphosis. At the developmental stage at which the hemolymph of the unparasitized metamorphosing host has its maximum titer of prepupal ecdysteroids, the hemolymph of 4th instar "truly parasitized" hosts (hosts with a surviving endoparasite) had a strongly reduced ecdysteroid titer. However, during the photophase about 12 h later, just prior to emergence of the parasite larva, an ecdysteroid peak was observed in the host hemolymph. Fourth instar pseudoparasitized prepupal hosts (in which the endoparasite was not present or died early in development) exhibited a sustained suppression in the hemolymph ecdysteroid titer. Small 5th instar pseudoparasitized hosts, which normally would molt to a 6th instar prior to metamorphosis, but which precociously attained the prepupal stage, also had a strongly reduced ecdysteroid titer. The late increase observed in truly parasitized hosts could be completely prevented by surgical removal of the parasite 24 h earlier, resulting in a titer similar to that in pseudoparasitized hosts. HPLC analysis of ecdysteroids in normal, truly parasitized, and 4th or 5th instar pseudoparasitized prepupae showed that both ecdysone and 20-OH ecdysone* were suppressed in truly and pseudoparasitized prepupae, with ecdysteroid levels being lowest in pseudoparasitized hosts. These data, and those of Brown and Reed-Larsen (Biol Contr 1, 136 [1992]), showing endoparasite secretion of ecdysteroids just prior to its emergence from the host, strongly indicate that: (1) the prepupal peak in truly parasitized hosts originates from the endoparasite, and (2) the low level of ecdysteroids in pseudoparasitized hosts results from the host's intrinsic inability to express a normal level of prepupal ecdysteroid titer. While precocious 4th or 5th instar prepupae of similar size had similarly suppressed ecdysteroid titers, smaller 4th instar prepupae had a lower ecdysteroid titer than larger, precocious 5th instar prepupae. Rare 5th instar pseudoparasitized prepupae that were of nearly normal size showed a prepupal ecdysteroid titer distinctly greater than those of the usual smaller, precocious 5th instar prepupae. The data suggest that the competence of the host to express a normal hemolymph titer of prepupal ecdysteroids is more closely correlated with the size of the prepupae than with the instar attained.
利用一种寄生蜂（近似弯斑茧蜂）研究了鳞翅目预蛹中蜕皮甾体产生的调控，这种寄生蜂在诱导宿主早熟变态后能特异性抑制宿主预蛹期蜕皮甾体的产生。在未被寄生的变态宿主血淋巴中预蛹蜕皮甾体滴度达到最高的发育阶段，四龄“真正被寄生”宿主（体内有存活内寄生幼虫的宿主）的血淋巴中蜕皮甾体滴度大幅降低。然而，大约12小时后的光照阶段，就在寄生幼虫羽化前，在宿主血淋巴中观察到一个蜕皮甾体峰值。四龄假寄生预蛹宿主（体内不存在内寄生幼虫或内寄生幼虫在发育早期死亡）的血淋巴蜕皮甾体滴度持续受到抑制。小型五龄假寄生宿主，正常情况下在变态前会蜕皮至六龄，但早熟进入预蛹阶段，其蜕皮甾体滴度也大幅降低。在真正被寄生的宿主中观察到的后期升高现象，如果提前24小时手术摘除寄生虫，可被完全阻止，导致滴度与假寄生宿主相似。对正常、真正被寄生以及四龄或五龄假寄生预蛹中的蜕皮甾体进行高效液相色谱分析表明，真正被寄生和假寄生预蛹中的蜕皮酮和20 -羟基蜕皮酮*均受到抑制，假寄生宿主中的蜕皮甾体水平最低。这些数据，以及布朗和里德 - 拉森（《生物防治》1，136 [1992]）的数据，显示内寄生幼虫在从宿主羽化前会分泌蜕皮甾体，有力地表明：（1）真正被寄生宿主中的预蛹峰值源自内寄生幼虫，（2）假寄生宿主中蜕皮甾体水平低是由于宿主自身无法表达正常水平的预蛹蜕皮甾体滴度。虽然类似大小的早熟四龄或五龄预蛹的蜕皮甾体滴度同样受到抑制，但较小的四龄预蛹的蜕皮甾体滴度低于较大的早熟五龄预蛹。罕见的接近正常大小的五龄假寄生预蛹的预蛹蜕皮甾体滴度明显高于通常较小的早熟五龄预蛹。数据表明，宿主表达正常血淋巴预蛹蜕皮甾体滴度的能力与预蛹大小的相关性比与所达到的龄期更密切。
