Acta Entomologica Sinica ›› 2021, Vol. 64 ›› Issue (7): 851-861.doi: 10.16380/j.kcxb.2021.07.009

• RESEARCH PAPERS • Previous Articles     Next Articles

Fine structure of silk glands of Capnogryllacris nigromarginata (Orthoptera: Gryllacrididae)

DOU Yu-Jie, ZHAO Hui-Min, SHI Fu-Ming, CHANG Yan-Lin*   

  1.  (College of Life Sciences, Hebei University, Baoding, Hebei 071002, China)
  • Online:2021-07-20 Published:2021-08-02

Abstract: 【Aim】 Raspy crickets (Orthoptera: Gryllacrididae) are a unique group in the Orthoptera, and they produce silk and use it to build shelters. The purpose of this study is to investigate the structural characteristics of their silk glands. 【Methods】 The fine structure and ultrastucture of silk glands of Capnogryllacris nigromarginata were observed by anatomy observation, immunofluorescence, hematoxylin-eosin staining, PAS-hematoxylin staining, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 【Results】 The silk glands of C. nigromarginata are composed of acini and silk ducts. Each acinus is composed of a fibrous sheath enclosing four main types of cells: type Ⅰ secretory cells, type Ⅱ secretory cells, peripheral cells and canal cells. Type Ⅰ and Ⅱ secretory cells are large glandular cells in irregular shape. The secretory cells have large nuclei. The cytoplasm of secretory cells is characterized by containing abundant endoplasmic reticulum and secretory particles. Type Ⅰ secretory cells are near the center of acinus. PAS-hematoxylin staining showed that type Ⅰ secretory cells contain glycoprotein. Type Ⅱ secretory cells are at the peripheral region of acinus located between type Ⅰ secretory cells and peripheral cells or sheath cells. The canal cells are scattered between the secretory cells and form the extracellular transport canal of secretion. In contact with the sheath cells, peripheral cells have microvilli cavity formed by cell membrane invagination, and there are a large number of mitochondria in the cytoplasm. The microvilli cavity is connected to an extracellular canal surrounded by canal cells. Secretory particles are accumulated at the junction of the secretory cells and the extracellular transport canal. Then they discharge secretions to the extracellular transport canals. The extracellular canals of multiple acini converge to the silk duct composed of a single layer of cells. The cell periphery of the silk duct is involved in the organization of a series of deep invaginations of the plasma membrane. A large number of elongated mitochondria can be observed around the cell plasma membrane invaginations. The apical border of the silk duct cell near the inner lumen has continuous membrane processes that are closely aligned under the cuticle of the duct wall. 【Conclusion】 The secretory cells of silk glands of C. nigromarginata can be divided into type Ⅰ and type Ⅱ secretory cells. The production and secretion process of secretory materials in turn pass through secretory cells, extracellular canals of canal cells, branch ducts, common duct of silk glands, and salivarium. When the secretions are transported outward from the extracellular canal surrounded by the canal cells, the microfilaments in the microvilli cavity of peripheral cells may provide impetus for the excretion of secretions.

Key words: Orthoptera; Capnogryllacris nigromarginata, silk glands, microstructure, ultrastructure