The Internal Organs Of Scale Insects And The Development Of Parasitic Wasps Within Its Host Body

The scale insects belong to Coccoidea of Hemipetera in Insecta, and about 7000 species in 20 families was recorded in the world. They are one group of the most important pests in agricultural corps, forests, fruit trees and ornamental plants. The special characteristic of scale insects is substance covered the surface of the body with various dermal glands in integument which can secrete waxiness to protect themselves. It is of great significance to research on the structure of integument and wax glands, internal organs and physiological metabolism, as well as the function that related to secreting wax for deeply understanding biology, physiology, phylogeny, evolution and biological control of the scale insects. But only a few studies were reported in China and abroad. In this thesis, two species of mealybug (Pseudococcidae), Phenacoccus fraxinus Tang, Pseudococcus comstocki Kuwana, and three species of soft scale insects (Coccidae), Ceroplastes japonicus Green, Eulecanium gigantean Shinji and Eulecanium kuwanai Kanda, were studied. Their fine and ultra-structure of the integument and internal organs were observed by using standard histological examination of serial sections of tissues embedded in paraffin and scanning electron microscopy. At the same time, the development of a parasitoid Encyrtus sasakii Ishii (Hymenoptera: Encyrtidae) in the body of the scale insect, Eulecanium kuwanai, was also studied. Results are summarized as follow:1. Structure of integument The integument of scale insects was composed of three main layers, procuticle, epidermis and basement membrance. The procuticle located in outermost integument layer consisted of epicuticle, exocuticle, endocuticle and formation zone. Epicuticle, exocuticle, endocuticle are not cell, but chitin, protein, fat, and pigments in chiefly. Formation zone was a layer of cells that were ranged one next one closely and small in diameter. A layer of cells lying immediately beneath the formation zone, epidermis, was the thickest layer in the integument in which wax gland cells, trichogen and tormogen were growing. Wax glands cells were big complex cells, round or apple-like with 20μm in diameter. They were ranged closely and occupied most space of epidermis. The complex cell of trilocular pore was composed of 3 chambers, including one central cell and two lateral cells. The central cell possessed a reservoir where wax substances contained and an irregulary-shaped receptor ductule through which the waxiness could be secreted out. Similarly, the complex cell of quinquelocular spiracular disc-pore consisted of 5 chambers, as well as multilocular disc-pore with multiple chambers. Tri-, quinque-, and multilocular disc-pore all possessed a short canal through which the wax could be secreted out. And multilocular disc-pore possesses of shortest one. However, canal of tubular duct gland was long, consisting of a inner ductule that extended its tip receptor and a outer ductule which extend its pore to surface of the epicuticle.2. Digestive and excretory systemThe digestive system consisted of mouth, pharyux, oesophagus, salivary gland, fore-gut, mid-gut, hind-gut and gastric caecum. Fore-gut was thin and membraneous; mid-gut was thick, long and loop-shaped with a thick wall. The gut wall cells were big with clearly nucleus. A pair of grape-like salivary gland situated on the both sides of pharynx were well-developed. Excretory system consisted of hind-gut, filter chamber, malpighian tubule and anus. Hind-gut was thick and membraneous. Filter chamber with 6 shell-like outgrowth on the surface wrapped at anterior of hind-gut. Malpighian tubule were two, yellow, resembling a string of beads and grown at the joint inter of mid-gut and hind-gut. The inner of malpighian tubule looked like faviform. The inner layer of digestive tube evenly formed hump or protuberance to increase the surface area for absorption of nutrient.3. Respiratory and tracheal systemThe respiratory and tracheal system of scale insects were different of other insects. There were only two pairs of spiracles situated latero-vetrally on the meso- and metathorax. 8-15 chief tracheae clustered in each spiracle. The chief tracheae splited gradually in 2 branches, and formed tracheal network to transport the oxygen to all parts of the body. The wall of tracheae were transparent with clearly taenidia. There was some water in the internal of trachea.4. Female reproductive systemThe ovary of scale insects had paired lateral oviducts comprised of two lateral oviduct, vagina, spermatheca and vulva. The mature ovary was paired, Y-shaped, and yellow in color. It occupied almost the entire body of the adult female. Each lateral oviduct comprised of numerous short ovarioles. Each ovariole consisted of one trophic chamber, one egg chamber and one pedicel which connected to the bottom of the egg chamber. Three nurse cells were observed in the trophic chamber, while yolk, lipid droplets and an oocyte were seen in the egg chamber. Follicular cells were arranged along the wall of the egg chamber and extended to form the pedicel. Many tracheae and tracheoles of various thicknesses were observed innervating the clusters of ovaries.5. Development of parasitic wasps within its host bodySeveral Encyrtus sasakii Ishii parasite in the body of Eulecanium kuwanai. They reproduce annually and hibernates as pupa in host. The egg had a long breath pedicle at one end. The larvae from the 1^st to 4^nd instar all had the long breath pedicles in the end of abdomen. And with the larva molting during development, the exuvia accumulate at the end of the body, formed a hollow sac called caudal sac that covered the breath pedicle during 3^rd and 4^th instar larvae. The pupae still had the caudal sac. The scutulis of female adults were yellow, and foreside of wings was light fumed with a dark blotch covered by dense black thick hairs. While the male adults were black brown, the wing was light color without a dark blotch.