Embryogenesis of the Sand Fly Phlebotomus papatasi (Diptera: Psychodidae): Organogenesis of the Nervous System, Tracheal System, Muscular System, Heart, and Gonad Rudiments

Abstract

Formation of the embryonic brain of the sand fly Phlebotomus papatasi (Scopoli) starts at 108 h after oviposition with proliferation of the ectodermal cells in the posterior region of the blastocephalon. Within 156 h, the brain is completely formed. The subesophageal ganglion is formed by 156 h. The basic form of the ventral nerve cord is initiated at 84 h with migration of the neuroblasts from the ectodermal layer. These cells form the ganglionic lobes, which become fully differentiated by 156 h and form a chain of 3 thoracic and 8 abdominal ganglia. Eye rudiments appear at 132 h and become fully differentiated by 156 h. Cuticle surrounding all appendages and body segments is secreted by ectodermal cells between 132 and 168 h. Rudiments of the tracheal system begin to differentiate at 120 h, becoming well-defined tracheae and longitudinal trunks by 168 h. Formation of the musculature of the gnathal segments begins at 144 h and is completed during the course of embryogeny. The true musculature is formed from the somatic mesoderm, which also gives rise to the heart. The ventral and dorsal longitudinal muscles begin to form at 132 h an are completed by 168 h. A tubular heart is seen at 168 h. The gonadal rudiments are formed by 144 h in the midlateral position of abdominal segments 6 and 7. Each rudiment consists of 6-8 pole cells that are surrounded by a layer of splanchnic mesodermal cells. The pole cells in each rudiment begin mitosis at 180 h; by 204 h the total number of cells in each rudiment is attained (6-10). No other part of the reproductive system is formed during embryogeny of the egg stage.