Morphology and Ultrastructure of the Alimentary Canal of Oriental Fruit Fly Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) (I): The Structure of the Foregut and Cardia

membrane and it is surrounded by a well-developed visceral circular muscle. The cardia is located between the foregut and the midgut, and includes the midgut epithelium in the outer portion of the cardia and the foregut epithelium in the inner portion. The oesophageal epithelium extends into the cardia to form the cardial valve. Both the longitudinal and the circular muscles beneath the oesophageal epithelium form a sphincter to control the entrance of food to the midgut and prevent the regurgitation of the midgut contents. The peritrophic membrane is secreted and forms from the surface of microvilli of the midgut at the anterior part of the cardia.