Salivary glands of second and third instars of Dermatobia hominis (Diptera: Oestridae).

Salivary glands of Dermatobia hominis (L., Jr.) (Diptera: Oestridae) larvae were studied under light and electron microscopy. The salivary glands of second (L2) and third instars (L3) are similar and consist of pairs of translucent tubules. The individual efferent ducts unite to form a single deferent duct, which inserts dorsally into the cephalopharingeal skeleton. Each gland has a monolayer of epithelial cells surrounded by basement membrane and connective tissue. The cellular plasma membrane is enfolded at its base, forming a labyrinthine area. The cell surface is linked to the basement membrane (BM) by hemidesmosomes and to adjacent cells by septet junctions and desmosomes. Irregular channels with several vesicles occur between the cytoplasm and BM. Golgi complex, rough and smooth endoplasmic reticulum, ribosome, lysosomes, multivesicular bodies, and myelin figures are usually present in the cells. The nucleus is large, with diffuse chromatin. The connective tissue circling the BM contains collagen fibrils, muscle fibers and tracheal tubes. Lined cuticle encloses the efferent and deferent ductal cells, which have few, widely dispersed mitochondria, free ribosomes, microtubules, and a large nucleus with diffuse chromatin.

Optical and ultrastructural studies of midgut and salivary glands of first instar of Dermatobia hominis (Diptera: Oestridae).

Midguts and salivary glands of newly hatched larvae (L1) of Dermatobia hominis (L., Jr.) were studied using light and electron microscopy. The larval midgut has a tubular, sinusoidal form and consists of a monolayer of epithelial cells with an underlying basement membrane and a surrounding layer of connective tissue. The fine structure of the midgut shows digestive cells with short microvilli, large nuclei, and cytoplasm containing few visible organelles (mitochondria, rough endoplasmic reticulum, and free ribosomes). In the basal region, the plasma membrane of the cells is folded into a labyrinth area. Hemidesmosomes link the basal surface to the basement membrane and septet junctions are present between adjacent cells. The connective tissue circling the basement membrane contains collagen fibrils, muscle fibers, and tracheal tubes. Prominent nuclei with evident nucleoli occur in the digestive cells. The salivary gland is simple and tubular. It has a monolayer of epithelial cells surrounded by basement membrane and connective tissue. The fine structure of the salivary gland shows epithelial cells, microvilli, secretion into the lumen, septate junctions at the lateral face and a basal labyrinth region. The cell nucleus is large and the cytoplasm contains rough endoplasmic reticulum, ribosomes and mitochondria.

Midgut ultrastructure of the third instar of Dermatobia hominis (Diptera: Cuterebridae) based on transmission electron microscopy.

The midgut ultrastucture of the third-instar of Dermatobia hominis (L., Jr.) was investigated using transmission electron microscopy (TEM). The tubular midgut bears a monolayer of epithelial cells with the plasma membrane showing multiple folding where it adjoins the basement membrane. Septate junctions bound the epithelial cells on each side. These cells have electrolucent cytoplasm containing mitochondria, vacuoles, rough and smooth endoplasmic reticula, lamellar bodies, and a prominent nucleus with dispersed chromatin. The peritrophic matrix is close to elongate microvilli, which are sometimes forked. Regenerative cells, in an undifferentiated state when closest to the basement membrane, are scattered throughout the epithelial cells. A thick basement membrane, surrounded by thick connective tissue including muscle, tracheal tubes, and extracellular matrix is linked to epithelial cells by hemidesmosome-like structures. Entero-endocrine, goblet or cuprophilic cells were not observed.

Activated host neutrophils in the larval midgut lumen of the human bot fly Dermatobia hominis.

Light microscopy (LM) and transmission electron microscopy (TEM) were used to observe activated polymorphonuclear neutrophils from mammalian hosts as well as invading bacteria in the midgut lumen of larvae of the human bot fly Dermatobia hominis. Other resident or recruited cells associated with dermal myiasis were fed on by larvae and digested more rapidly than neutrophils. The latter were observed moving towards bacteria and particles of food, extending the filopodia and engulfing material to be digested within phagosomes. The larval midgut lumen, thus, appears to be a suitable environment to produce neutrophil activation at least for short periods, as seen in mammalian hosts. Although interactions between phagocytes and bacteria in the midgut lumen may be important in bot fly larval development, further studies are required to confirm this.

Histochemical localization of N-acetyl-galactosamine in the midgut Lutzomyia longipalpis (Diptera: Psychodidae).

The binding of lectins to the midgut of the female sand fly Lutzomyia longipalpis (Lutz & Neiva) was investigated using lectin-gold conjugates. Midguts from laboratory-reared flies provided fructose solution and/or blood fed on hamster were dissected at 6, 24, and 48 h and at 5 and 7 d after feeding. Before examination by transmission electron microscopy, each midgut was sectioned, incubated with lectins from four sources (Canavalia ensiformis [ConA], Helix pomata agglutinin [HPA], peanut agglutinin [PNA], and wheat germ agglutinin [WGA] ), then conjugated with colloidal gold. Only HPA, which is specific for N-acetyl-galactosamine (GalNAc), bound to the midgut. Binding sites were cytoplasmic secretory granules and microvilli throughout the length of the midgut epithelium. Binding occurred in sand flies fed fructose as well as in flies receiving a blood meal. The presence of GalNAc on the midgut microvilli of sand flies before, during, and after blood feeding indicates this amino-sugar is not altered by digestion. As a structural component, GalNAc may represent a terminal on a receptor molecule. The failure of the sand fly peritrophic matrix to bind WGA by N-acetylglucosamine may be caused by the complex composition of the membrane, which renders N-glycan inaccessible to the lectin-gold conjugate.

Ultrastructure of endocrine cells from the abdominal midgut epithelium of Lutzomyia longipalpis (Diptera: Psychodidae).

Transmission electron microscopy (TEM) was used to study two types of endocrine cells front the midgut of adult female Luttzomyia longipalpis (Lutz & Neiva). Endocrine cells rarely have been observed in Nematocera, even using TEM, and were present in small numbers dispersed among the monolayer of midgut digestive epithelial cells. Triangular shaped "closed" cells were observed along the basement membrane, bounded on each side by digestive cells; these cells closed distally before reaching the epithelial lumen. These endocrine cells appeared to deliver active granules that were secreted through a cellular membrane into the hemolymph. A second cell type occupied a similar position to the closed cells, but opened into the midgut lumen via microvilli, where the secretory products may be delivered. Each cell type possessed both electron-lucent and electron-dense vesicles with secretory granules which may indicate different stages in maturation and activity. These granular secretory products are probably peptidergic substances, with secretion mediated by diet via basal and baso-lateral receptors that were bound to membranes or microvilli.

Scanning electron microscope observations on third-instar Gasterophilus nasalis (Diptera: Oestridae).

Scanning electron microscope observations studied the morphology of 3rd-instar Gasterophilus nasalis (L.). Distinctive features are illustrated in a sequence of 16 micrographs, bearing indications of structures considered of special interest. The morphology of G. nasalis is compared with that of other larval bot flies.