Zoological Studies

Morphology and Ultrastructure of the Alimentary Canal of the Oriental Fruit Fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) (2): The Structure of the Midgut

Chun-Nu Hung, Tai-Lung Lin and Wen-Yung Lee (2000) The midgut of Bactrocera dorsalis (Hendel) was studied by using light and transmission electron microscopy. The midgut of this insect, the longest part of the entire alimentary canal, is about 16 mm in length. Its anterior portion is shaped as a tube located in the haemocoel of the thorax, while the most distal part is coiled and embedded in the first three abdominal segments. The midgut epithelium is characterized by a striated border of microvilli, and 2 layers of the peritrophic membrane lie in the gut lumen to protect the midgut cells from possible damage from abrasive food particles. The epithelium is surrounded by 2 layers of muscles and comprised of 4 different types of cells: columnar, goblet, interstitial, and regenerative cells (or nidi). Columnar cells comprise the majority in the epithelium, while a few goblet cells associated with the interstitial cells are found in the middle part of the midgut. Regenerative cells are undeveloped cells lying as a group at the basal portion of the epithelial cells. The structure and function of secretion of digestive enzymes and absorption of nutrients in the midgut epithelium of this fly are discussed.