Morphological Differentiation of the Eggs of North American Container-Inhabiting Aedes Mosquitoes.

Aedes aegypti , Ae. albopictus, Ae. japonicus japonicus, and Ae. triseriatus eggs are described with the aid of color images and images from scanning electron microscopy. All eggs were broadly cigar shaped with Ae. triseriatus and Ae. j japonicus eggs being dull or matte black, while Ae. albopictus and Ae. aegypti eggs were shiny jet black. Aedes triseriatus eggs were lighter in color and had a rougher appearance when compared to those of Ae. j. japonicus. Aedes albopictus and Ae. aegypti eggs can be differentiated by the distinct presence of micropylar collars in Ae. aegypti. Our results reduce the need to rear these mosquitoes, reducing labor and time while providing an accurate identification of the vector mosquitoes.

MIDGUT ULTRASTRUCTURE OF FOURTH INSTAR OCHLEROTATUS TOGOI (DIPTERA: CULICIDAE).

The ultrastructure of the midgut of fourth instar Ochlerotatus togoi was investigated by light, scanning and transmission electron microscopy. This study was performed to provide information to help devise future control efforts aimed at the larval stages of this vector of filariasis. The fourth instar midgut was approximately 2 mm in length and consisted of three morphologically distinct cell types: epithelial, regenerative, and endocrine cells. There was a monolayer of epithelial cells on the luminal surface of the midgut, with multiple folds of the plasma membrane where it adjoined the basement membrane. Regenerative cells were scattered throughout the basal portion of the epithelium, along with endocrine cells. No evidence of division or differentiation was seen in any of the cell types. Six layers of the peritrophic matrix were observed in the gut lumen which separated ingested food from the midgut epithelial cells. Cytoplasmic protrusions were seen in many areas of the luminal midgut surface and numerous autophagosomes were seen in the epithelial cells of both early and late fourth instar larvae, suggesting autophagy is involved in the degeneration process of the midgut in preparation for pupation. This study provides a basis for understanding normal Oc. togoi larval midgut development. Further studies are needed to determine the factors that control larval growth and the nutritional state. Such information could be used to reduce adult fecundity and develop biological control mechanisms.

Peritrophic matrix formation and Brugia malayi microfilaria invasion of the midgut of a susceptible vector, Ochlerotatus togoi (Diptera: Culicidae).

The mosquito midgut is the first site that vector-borne pathogens contact during their multiplication, differentiation, or migration from blood meal to other tissues before transmission. After blood feeding, the mosquitoes synthesize a chitinous structure called peritrophic matrix (PM) that envelops the blood meal and separates the food bolus from the midgut epithelium. In this study, a systematic investigation of the PM formation and the interaction of Brugia malayi within the midgut of a susceptible vector, Ochlerotatus togoi, were performed using scanning electron microscopy (SEM). SEM analysis of the midguts dissected at different time points post feeding on a B. malayi-infected blood meal (PIBM) revealed that the PM was formed from 45 min PIBM and gradually thickened and matured during 8-18 h PIBM. The PM degraded from 24 to 72 h PIBM, when digestion was completed. The invasion process of the microfilariae was observed between 3 and 4 h PIBM. In the beginning of the process, only sheathed microfilariae interacted with the internal face of the PM by its anterior part, and then the midgut epithelium before entering the hemocoel, after that they exsheathed. Microfilarial sheaths lying within the hemocoel were observed suggesting that they may serve as a decoy to induce the immune systems of the mosquitoes to respond to the antigens on the sheaths, thereby protecting the exsheathed microfilariae. These initial findings would lead to further study on the proteins, chemicals, and factors in the midgut that are involved in the susceptibility of O. togoi as a vector of filariasis.

Scanning electron microscopy of the egg of Ochlerotatus albifasciatus (Diptera: Culicidae).

Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) is a mosquito species of medical and veterinary importance, usually associated with temporary groundwater habitats. Eggs obtained from females collected in Córdoba city, in the center of Argentina, were studied using scanning electron microscopy. The eggs are elliptical in outline, measuring approximately 615.7 +/- 37.24 microm in length (1) and 180.7 +/- 22.87 microm in width (w), with an egg index (l/w ratio) of 2.9-3.7. The outer chorionic sculpture has racquet-shaped and wristwatch-shaped cells consisting of a small central tubercle surrounded by larger tubercles and followed by a row of smaller tubercles on one or both sides, respectively, although variations between regions of the egg were observed. The micropylar apparatus has a collar with evident molding and edges of determined length, albeit irregular, with defined margins for the transition area and a thickness of approximately 10.7 microm. The margins of the micropylar disc are raised and the disc measures approximately 21.1 microm in diameter. The micropyle is distinct.

Description of the egg of Ochlerotatus japonicus japonicus (Diptera: Culicidae) using variable pressure scanning electron microscopy.

The egg of Ochlerotatus japonicus japonicus (Theobald) is described with the aid of variable pressure scanning electron micrographs. The egg is black, cigar shaped, and tapers ventrally. The length is approximately 591 microm and the width is approximately 172 microm. The outer chorionic cells are irregular in shape, either hexagonal or pentagonal, and decrease in size toward the anterior and posterior poles. Ventral tubercles typically range from three to six and contact the chorionic reticulum. Dorsal tubercles contain two large tubercles with small oval-shaped tubercles grouped around them. A large thread-shaped tubercle extends from this grouping either as a single tubercle or as a series of connected tubercles. The micropylar collar is low and discontinuous and is seldom complete. This description will aid researchers in the identification of this invasive vector species.

Scanning electron microscopy of eggs of Ochlerotatus (Protomacleaya) terrens Walker.

Observations on the morphological ultrastructure of eggs of Ochlerotatus (Protomacleaya) terrens (Diptera: Culicidae) were conducted by using scanning electron microscopy. Morphometry of the principal structures was obtained with the aid of Semafore analysis software. Eggs of Oc. terrens from females caught in the Biological Reserve of Tinguá, State of Rio de Janeiro, Brazil, were utilized. The eggs presented elliptical outlines, with a length of approximately 649.0 microm and width of 168.7 microm. The egg index (length to width ratio) was 3.85 microm. The exochorion had hexagonal and sometimes pentagonal ornamentation. Inside the chorionic cells were small, well-distributed tubercles with a large range of sizes. The micropylar apparatus, located in the anterior region of the egg, presented a collar with a poorly visible frame, with borders of indeterminate extent and margins without a defined transition area, and a thickness of approximately 1.8 microm. The micropyle was plugged.