Structure Of The Alimentary Canal And Reproductive System Of Adult Dendroctonus Armandi (coleoptera: Scolytinae)

The Chinese white pine beetle, Dendroctonus armandi (Coleoptera: Scolytinae) as a pioneer of bark beetles'ecosystem in Qinling Mountains, is specifically destroying Chinese white pine Pinus armandi. So it is seriously harmful to ecological stability of forestry in Qinling–bashan Mountains. The research was fully carrying out on the life history, mechanism of invading host tree, pheromone, flight and dispersal, the relation with their symbiosis and so on. However, the studying on their population fluctuation and mechanism of the Chinese white pine destroyed by D. armandi, as well as the exploration of the technical management in D. armandi will be directly limited because of failure of basic research on structure of alimentary canal and reproduction and population growth. Hence, we closely focused on the basic study on bark beetle's digestion and reproduction to reveal the mechnism of their population fluctuation. We clarified its adaption to nicho under bast from the aspect of the morph-function of alimentary system and reproductive system by using SEM, TEM and so on. The results are as follows:1. The morphology and histology of the alimentary canal of the Chinese white pine beetle were studied by means of light and electron microscopy. The alimentary canal composed of foregut (formed by oral cavity, pharynx, esophagu, crop and proventriculus), midgut (formed by the anterior, posterior and 160 gastric ceca) and hindgut (formed by the anterior, posterior and 6 tuba Malpighii). Although many structures, such as 6 tuba Malpighii, the cryptonephridial system, spines in the esophagus and crop and chitinous plates in the proventriculus, were found to be similar to those reported for other Dendroctonus Erichson species, some differences were apparent, such as 6 row gastric ceca in the midgut, longitudinal muscle in the hindgut, fine spines on the hindgut cuticle, and specialized proventricular plates.2. The longer microvilli, abundant the rough endoplasmic reticulum (RER), and the folds of the basal labyrinth strongly existed in the epithelium of the posterior of midgut. Meanwhile, peritrophic membrane, which belonged to typeⅡ, was 2 layers tubiform with buttons-like structure every 1um in its surface. The hindguts structural characteristics, such as the cuticle in the surface of epithelium, the absence of microvilli, the scarce amount of organelles, and the thick muscle tissue, suggested that absorption and synthesis processes should be lower in this region than in the midgut. Also, more RER and redundant granules with strong electron dense were present in the epithelial cells of the midgut from the mature female individual. It indicated that Endodermal or midgut cells function as the site of pheromone synthesis.3. Proventriculi morphology was studied in 16 species of bark beetles (Coleoptera: Scolytinae) representing two subfamilies from host tree (Pinus armandi Fr.) by using light microscopy and scanning electron microscopy. General Proventricular morphology was found to be similar for those of species analyzed, with the presence of eight thick cuticular plates. Each chitinous plate can be divided in an anterior plate with sclerotized appendices formed by denticles or spines, and a masticatory plate with the movable brushes and long fine bristles. Obvious differences were observed in the sclerotization degree, the shape of the anterior plate and type of sclerotized appendices among the different bark beetles groups. Three types of proventriculus were identified according to the basic morphous comparison of the chitinous plates, and their morphology may supply auxiliary characters for taxonomy of these bark beetles. Obvious morphous variation and the sclerotization level of proventriculus may reflect an adaptation to variations in diet, which lead to occurrence of spatial and time sequence for 16 bark beetles in P. armandi.4. The reproductive tract and Spermiogenesis in Chinese white pine beetle were investigated by light and electron microscopy. The reproductive tract was composed of testes, deferent ducts, seminal vesicles, strand-shaped accessory glands, curcled accessory gland per unit and one common ejaculatory duct. The differentiation of spermatids occured within cysts of up to 512 germ line cells each one. While the spermatozoon and spermiogenesis was shown to possess several traits that are characteristics of other beetles in general. The head was formed by a three-layered acrosome with the perforatorium, the acrosomal vesicle, the extra-acrosomal layer and the nucleus. The flagellum presented a typical axoneme with a 9 + 9 + 2 microtubule pattern, two accessory bodies and two mitochondrial derivatives, which appeared with different sizes. In both derivatives there were dense crystalloid regions. Some peculiar characteristic were noted: the presence of tridents shaped nucleus in early spermatid stage, the presence of"h"shaped acrosomal visicles, a puff-like structure, the centriole derivative and a loose"large coil"-like spony body structure in sperm. Furthermore, the occurrence of 20 tubules and two type accessory glands in D. armandi differed from other Coleopteran so far examined.5. The present study described the female reproductive tract and the ultrastructure of meroistic telotrophic ovaries of the bark beetle D. armandi. The female reproductive system consisted of four ovaries and two short lateral oviducts, one oviduct and a spermatheca, devoid of the accessory glands. In this type of ovary, from apex to base individual ovarioles had four well defined regions: a terminal filament, tropharium (trophic chamber), vitellarium and pedicel (ovariolar stalk). Tropharia were not differentiated into distinct zones and consist of syncytium containing multiple trophocyte nuclei embedded in a common cytoplasm. Early previtellogenic (arrested) oocytes and prefollicular cells were located at the base of the tropharium. The vitellarium housed linearly arranged developing oocytes each of which was connected to the trophic core by a broad nutritive cord. Each oocyte was surrounded by a single layer of follicular cells. For D. armandi in the emergence phase, oocytes only in pre-vitellogenic and vitellogenic stages were observed in the vitellarium. Along with the developing of oocytes, the larger intercellular spaces, more redundant mitochondria and RER in the follicular epithelium were present than those observed in the previous stage. Our data clearly indicated that the opening of these spaces in the follicular epithelium of D. armandi oocytes increased as the intake of exogenous proteins intensifies, that was, in middle and end stages of vitellogenic oocytes. Also, the follicular epithelium participated in the synthesis of pre-vitelline membrane. Meanwhile, more yolk granules and lipid droplets with the larger sizes in the oocytes were than those observed in the previous stage. There was rich in Golgi apparatus, RER and mitochondria in the cytoplasm of oocyte, which showed the oocyte itself, participated in the synthesis of yolk. A peculiar characteristic was noted that redundant RER whorls which surrounded large characteristic lipid droplets or protein were present in the end stage of vitellogenic oocytes.