Morphological and enzymatic analysis of the midgut of Anopheles darlingi during blood digestion.

The midgut of adult female Anopheles darlingi is comprised of narrow anterior and dilated posterior regions, with a single layered epithelium composed by cuboidal digestive cells. Densely packed apical microvilli and an intricate basal labyrinth characterize each cell pole. Before blood feeding, apical cytoplasm contains numerous round granules and whorled profiles of rough endoplasmic reticulum. Engorgement causes a great distension of midgut. This provokes the flattening of digestive cells and their nuclei. Simultaneously, apical granules disappear, the whorls of endoplasmic reticulum disassemble and 3h post bloodmeal (PBM), nucleoli enlarge manyfold. An intense absorptive process takes place during the first 24 h PBM, with the formation of large glycogen inclusions, which persist after the end of the digestive process. Endoproteases activities are induced after bloodmeal and attain their maximum values between 10 and 36 h PBM. At least two different aminopeptidases seem to participate in the digestive process, with their maximum activity values at 36 and 48 h PBM, respectively. Coarse electrondense aggregates, possibly debris from digested erythrocytes, begin to appear on the luminal face of the peritrophic membrane from 18 h PBM and persist during all the digestive process, and are excreted at its end. We suggest that these aggregates could contain some kind of insoluble form of haem, in order of neutralize its toxicity.

Reduced juvenile hormone synthesis in mosquitoes with low teneral reserves reduces ovarian previtellogenic development in Aedes aegypti.

We investigated the relationship among nutritional reserves, previtellogenic ovary development and juvenile hormone (JH) synthesis in Aedes aegypti female mosquitoes. By raising larvae under different nutritional regimes, two adult phenotypes (large and small females) were generated, which differed significantly in size at eclosion (measured by wing length). We measured the total amount of protein, lipids and glycogen in newly emerged (teneral) large and small females. Teneral reserves were significantly lower in small females. Maximum previtellogenic ovary development occurred only if enough teneral nutrients were present. Maximum previtellogenic ovary development was stimulated in small females with low teneral nutrients by topically applying a JH analog. The biosynthetic activity of Ae. aegypti corpora allata (CA) was studied in vitro using a radiochemical method. JH synthesis was significantly reduced in females emerged with low teneral reserves and stimulated by sugar feeding. These results establish that the CA synthesizes enough JH to activate ovary maturation only in the presence of large nutrient reserves.

Free amino acids are important for the retention of protein and non-protein meals by the midgut of Aedes aegypti females.

There is a relationship between the normal progress of digestion and the retention or elimination of the proteins ingested with the meal by Aedes aegyti females. The addition of soybean trypsin inhibitor (STI) to a protein meal prevented digestion and resulted in a rapid elimination of the undigested proteins. The addition of a mix of free amino acids to a protein meal together with STI resulted in a significant increase in the retention of the undigested proteins during the first 10-15 hrs after feeding. The effect of the free amino acids on the retention of the proteins was concentration-dependent between 250 microg/ml and 5 mg/ml. Free amino acids were also important for the retention of non-protein meals. When females were fed a meal containing FITC-dextran (20 kD), most of this compound was eliminated into the feces by 10 hrs; the addition of free amino acid resulted in a significant increase in the retention of the FITC-dextran by the midgut during the first 15 hrs after feeding. The presence of free amino acids in the midgut lumen seems to be an important signal used by the mosquito to regulate the retention of the meal.