A study of the age structure of a population of adult female Aedes cantans Meigen was undertaken using the ovarian oil injection technique to determine parity. Results showed that, contrary to popular opinion, ovariolar sacs do not form gonotrophic dilatations and cannot be used for physiological age determination. Dilatations were formed only by follicles which degenerate at a very early stage in the gonotrophic cycle. The proportion which consistently do degenerate (the gonotrophic diagnostic index) decreases in each successive cycle. Results showed that the mean age of the population during the study was 2.04 parous, which was one gonotrophic cycle less than expected, possibly due to scarcity of hosts in the area.
A study of the age-dependent changes in the ovarioles and the age structure of a population of adult females of Anopheles gambiae in the Amani hills of north-eastern Tanzania was undertaken using the ovarian oil injection technique. The greatest difficulties encountered in accurately determining the age of members of this species are due to small size and the low parity diagnostic index of the ovary, which decreased in successive gonotrophic cycles and could drop to zero even in the first cycles. Additional information can be obtained from basal bodies, groups of six to eight cells in the calyx wall enclosed by the end of the ovariolar sheath. The possibility exists of their use for age grading of mosquitoes. The mean age of the population during the study, which was carried out in the rainy season, was rather low. The oldest were individuals that had completed four ovipositions. Among the mosquitoes infected with sporozoites were females that had completed between > 2 and > 4 ovipositions.
Age-dependent changes in the ovarioles of Simulium woodi (Diptera: Simuliidae) and the age structure of a wild population of this species in the Amani hills of north-eastern Tanzania were studied using the ovarian oil injection technique. Contrary to previous theories, egg sacs degenerate completely and do not form dilatations. The physiological age of the females could be determined only by gonotrophic dilatations formed from degenerating follicles during gonotrophic cycles. In individual females, the proportions of ovarioles with degenerating follicles were 3-54% (mean 22%) in the first cycle and 8-61% (mean 36%) in the second gonotrophic cycle. Agonotrophic degenerating follicles occurred in 2% of ovarioles in 12% of females. Additional information with regard to the degree of parity is given by the level of granulation in the basal body of each ovariole, a group of six to eight cells in the calyx wall enclosed by the end of the ovariolar sheath. Their granulation progressively increased in intensity following each subsequent ovulation.
Dissection of the ovaries of the mosquito Aedes aegypti (Diptera: Culicidae) revealed, in each ovariole, a group of seven to nine specialized epithelial cells in a region of the calyx wall that is enclosed by the end of the ovariolar sheath. This group of cells is termed the basal body. During ovulation, the mature oocyte passes from the ovariole into the calyx lumen through the basal body. Subsequently, granulation occurs in the basal body cells. The granular basal bodies differ from all previously described ovarian structures. In multiparous females the size and optical density of the granular basal bodies increase after each ovulation. Examination of the granular basal bodies in intact ovaries, stained with neutral red, provides an easy method for distinguishing parous from nulliparous females, and has potential as a new method of age grading.
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