斜纹夜蛾幼虫造血器官的形态、组织及超微结构

ANATOMY, HISTOLOGY AND ULTRASTRUCTURE OF THE HAEMO- POIETIC ORGANS OF SPODOPTERA LITURA

斜纹夜蛾Spodoptera litura Fabricius幼虫的造血器官位于翅芽部位,由发育层次不同的许多细胞岛和一些单个或成串的梭形细胞组成。各细胞岛或细胞均裹有一层非细胞性膜鞘。环绕同一翅芽的众多细胞岛和细胞相互间由其膜鞘连结成簇。膜鞘紧裹着的单个或成串梭形细胞具未分化细胞特征。发育初期的单个细胞岛体积较小,直径约20—45μm以下,岛内均为排列紧密的分化中未成形原血细胞。较发育的细胞岛体积较大,细胞间排列较松,岛内除原血细胞外,还出现少量浆血细胞、颗粒细胞和小球细胞的分化。此外,还发现一个具颗粒细胞和小球细胞特征的混合细胞类型。发育初期的细胞岛膜鞘表面结构完好。随着岛内细胞的增殖分化,膜鞘出现破裂,且破裂逐渐增大,以致完全破裂而裸露岛内细胞团,以此释放血细胞。大量血细胞释放出现于幼虫预备脱皮至下一龄幼虫初期的造血器官。各龄幼虫的各发育阶段血淋巴血细胞总数(THC)的变动与造血器官释放血细胞密切相关。

The histology and ultrastructure of the haemopoietic organs of the larvae of Spodoptera li- tura in fourth to sixth instars were examined with light, transmission and scanning electron microscopes. It was observed that each of the haemopoietic organs was composed of a number of spindle-shaped cells and many cellular islets of various size sheathed together with an acellular membrane adhering to the wing bud at its base. The spindle-shaped cells may be single or serial, and have a low ratio of cytoplasm to nuclei; and their cytoplasm contains few organ-elles, showing their embryonic nature. They are the stem cells of the haemopoietic organs and the new cellular islets are formed through their division. The young cellular islets assume compact form, with the prohaemocytes closely juxtaposed; while the more developmentally advanced islets are in reticulate form, as the intercellular connections gradually tend to disappear. A few differentiated plasmatocytes (PL), granulocytes (GR) and spherulocytes (SP) were found in the reticulate islets. A mixed type of cell with GR form at one end and SP form at another was also observed in the islet. The acellular membrane sheathing the islets is less than 50μm in thickness and continuous at the beginning; it gradually leaks as the volume of the islet increases during development; and finally it breaks down to expose blocks of cells to haemo-lymph. Then blood cells go into haemolymph from the blocks of cells. The total haemocyte counts (THC) in the haemolymph are closely related to the release of blood cells from the haemopoietic organs. Before and shortly after ecdysis, many blocks of cells could be found in the haemopoietic organs and the THC was high in the haemolymph. When the blocks of cells completely disappeared from the haemopoietic organs, the THC attained the highest value.