关键词: 豆大蓟马, 生长发育, 消化道, 比较形态学, 透射电子显微镜

Abstract: 【Aim】The aim of this study is to explicit the morphology and ultrastructure of the alimentary canal of the bean flower thrips, Megalurothrips usitatus at different developmental stages. 【Methods】 Confocal laser scanning microscope (CLSM) and transmission electron microscope (TEM) were used to observe the morphology and ultrastructure of the alimentary canal of nymphs, pre-pupae, pupae and adults of M. usitatus. 【Results】The alimentary canal of M. usitatus is composed of foregut, midgut, hindgut and Malpighian tubules. The mean length of the alimentary canal of the 1st instar nymphs, 2nd instar nymphs, pre-pupae, pupae, female adults and male adults are 1 642.65±158.68, 2 233.68±133.76, 1 264.39±92.43, 1 169.81±59.48, 2 380.32±196.67 and 1 344.31±143.29 μm, respectively. The foregut includes the pharynx, esophagus, crop and cardia.The intestinal wall is composed of the outer layer of myoepithelial cells, muscle layer, epithelial cell layer and cuticle from the outside to the inside. A large number of vesicles and inconspicuous cuticle were observed in the foregut of the 1st and 2nd instar nymphs. The cuticle of foregut cells in the prepupae, pupae and adults is thicker, and the muscles are also relatively developed. The midgut is divided into three parts, namely anterior, middle and posterior parts. The muscle cell layer and epithelial cell layer are distributed from the outside to the inside, and the side near the midgut lumen is specially formed into the microvilli structures.There are reserve materials in the anterior midgut cells of the 1st instar nymphs. Myelin-like structures and more autophagosome-like vesicle structures were observed in the anterior midgut cells of the 2nd instar nymphs. The concentric spherocrystal structures are widespread in the midgut cells of pre-pupae and pupae,and the basal labyrinth is obvious in the cells of the anterior and middle midgut of adults. The hindgut is composed of ileum and rectum, and has developed muscle layer and cuticle at each developmental stage. There is no muscle layer in the Malpighian tubules, but organelles or structures such as mitochondria, rough endoplasmic reticulum, basal labyrinth and zonulae adherens still exist in epithelial cells. No basal labyrinth structure was observed at the base of Malpighian tubules of pre-pupae and pupae, but multivesicular bodies are distributed in the pre-pupal Malpighian tubule cells. In addition, spherocrystal was observed in the cytoplasm of the pupal Malpighian tubules.【Conclusion】There are obvious differences in the morphological structure of the alimentary canal of M. usitatus at different developmental stages. In this study, according to the morphological composition, the functions of different parts of the alimentary canal were speculated as well. The results will provide experimental basis for further analysis of the morphology and functional differentiation of the alimentary canal of thrips.

Key words: Megalurothrips usitatus; growth and development, alimentary canal, comparative morphology, transmission electron microscopy