histochemistry to examine the distribution of the enzyme in the midgut of Aedes aegypti, Aedes albopictus, Culex quinquefasciatus, Culex nigripalpus, Ochlerotatus taeniorhynchus, Anopheles albimanus and Anopheles quadrimaculatus

Mosquitoes reproduce by laying eggs. While in some species both the male and female adults feed on nectar, only the female requires a blood meal in order to produce viable progeny. Upon feeding, the blood meal is stored in the midgut while meals of nectar are diverted to the crop (Clements, 1992). Not surprisingly, the midguts of adult females and males in these species present differences. The male midgut is smaller than the female midgut, although in both cases it consists of a narrow tube-like anterior region and a flaskshaped posterior portion surrounded by a delicate network of circular and longitudinal muscle cells along with trachea. Male and female midguts are composed of a single-cell epithelium consisting of three types of cells. Most of these cells are ‘columnar cells’, with smaller numbers of undifferentiated ‘regenerative cells’ and endocrine cells (Nuttal and Shipley, 1903; Thompson, 1905; Christophers, 1960). In terms of function, most of the attention has focused on the female midgut. Its function has been associated with storage and digestion of the blood meal, secretion of digestive enzymes and synthesis and secretion of the peritrophic membrane, nutrient absorption and diuresis (Clements, 1992). Blood feeding in turn, is linked to the transmission of viruses as well as Plasmodium and other parasites. Although the pH inside the larval midgut has been described in detail (Boudko et al., 2001; Charles and de Barjac, 1981; Dadd, 1975; Ramsay, 1950), a comprehensive study on the pH inside the adult mosquito midgut has not been presented. The importance of maintaining pH for physiological processes that occur inside the larval midgut and in survival of the larvae has been described recently (Boudko et al., 2001; Corena et al., 2002). Little is known about pH maintenance inside the adult mosquito midgut. Although the presence of trypsin and aminopeptidase, as well as esterases and chitinase, has been demonstrated in the adult mosquito midgut (Lemos et al., 1996; Mourya et al., 2003; Okuda et al., 2002; Villalon et al., 2003), there are no reports on the presence of CA and the role of this enzyme in the maintenance of pH inside the midgut. We have previously localized, cloned and measured CA content in the midgut of larval Ae. aegypti (Corena et al., 2002) as well as in other species of mosquito larvae (Corena et al., 2004). We have found differences in CA distribution among different species of larvae. However, mosquito larvae are morphologically and physiologically different from adult mosquitoes. The purpose of this study was to determine the pH, localize and measure CA content in the anterior and posterior midgut of adult male The Journal of Experimental Biology 208, 3263-3273 Published by The Company of Biologists 2005 doi:10.1242/jeb.01739