关键词: 舞毒蛾, 20-羟基蜕皮甾酮, 外部形态, 体壁, 超微结构, 透射电镜

Abstract: To ascertain the definite influence process of 20-hydroxyecdysone (20E) on cuticle, epidermic cells and cell organelle of integument in the molting process, transmission electron microscope was used to determine the influence of 20E on the integument ultrastructure of newly moulted 5th instar larvae of Lymantria dispar (Linnaeus). The results showed that larvae fed with white birch leaves soaked in high concentration of 20E ingested about 400 μg 20E when they stopped feeding within 6 h after treatment. At around 12 h post treatment, the microvilli on apical plasma membrane of epidermal cells reduced, and the ecdysial space started to form between the old cuticle and epidermal cells. The old head capsule started to break away from the larval head. At 24 h post treatment, the ecdysial space increased continually. The old cuticle separated further with epidermal cells and new cuticulin layer began to form. At around 36 h after treatment, short microvilli were formed at the apical plasma membrane, and a lot of electron lucent vesicles appeared at the cytoplasmic region. Epicuticle, exocuticle and about 8 layers of endocuticular lamellae were synthesized in the new cuticle. At 48 h after treatment, the bounds between apical plasma membrane and epidermal cells became obscure. Endocuticular lamellae were continuously synthesized to 16 layers. At 72 h post treatment, a large number of electron lucent vesicles appeared in the epidermal cells, and endocuticular lamellae were synthesized to about 20 layers. At 96 h after treatment, there were fewer organelles in epidermal cells of the treatment groups than in the control group. A small percentage of blank space occurred around nucleolus, and the contents in cytoplasm were reduced. The bodies of treated insects became nigrescence and shrinking, and they were close to death. The number of endocuticular lamellae maintained to be about 20 layers.In the control groups, however, at 6-96 h after treatment the larvae were active and fed normally, and no molting phenomenon was observed by external observation and transmission electron microscope experiments in these larvae. The cuticle of the larvae was composed of epicuticle, exocuticles and normal layers of endocuticular lamellae. The microvilli density was high. Those organelles were typical and active. The cell boundaries were visible in the cytoplasm area, where the inclusions are rich. The secretion activity of epidermal cell was vigorous, and the endocuticular lamellae increased continuously to 50 layers with increase of the treatment time. It is so inferred that 20E could lead to lethal moulting of 5th instar larvae of L. dispar.

Key words: Lymantria dispar, 20-hydroxyecdysone, external morphology, integument, ultrastructure, transmission electron microscopy