Clark, T.M.*; Hutchinson, M.J.; Moffett, D.F.: Apical surface morphology of the stomach region of the larval mosquito midgut.

Mature 4th instar larval Aedes aegypti measuring 6.5�0.19 mm in length have a stomach region of 3.3�0.18 mm (N=6). The stomach is clearly differentiated into distinct anterior, transitional and posterior regions (53.0�1.16%, 13.7�1.16%, and 33.3�0% of total stomach length respectively). The anterior stomach consists of cells that range from 5.7 to 44.4 mm in diameter (mean 28.6�1.68 mm). These cells are uniform in appearance and show a normal distribution by diameter. They have polygonal, flat apical surfaces with very short microvilli (0.4�0.02 mm). There are no intercellular clefts apparent at the level of SEM, rather the surface of the epithelium is smooth. The most anterior cells of the transitional region are similar in appearance to cells of the preceding anterior stomach region but have microvilli 1.2�0.03 mm in length. Microvillar length increases to 2.3�0.26 mm in the mid-transitional region, and to 4.2�0.25 mm in the posterior transitional region. The mean diameter of transitional region cells is 21.0�1.26 mm. The transitional region cells show a progression to a more rounded apical profile from anterior to posterior. Posterior stomach cells are characterized by globular protrusions of the apical surface that are separated by relatively deep clefts containing numerous microvilli, that were not observed in other stomach regions. Posterior stomach cell diameter is uniformly 19.7�1.08 mm throughout the anterior 2/3 of the posterior stomach (N=22) and increases to 26.2�1.45 mm (N = 8) in the posterior third of the posterior stomach region (P<0.0005).