Investigations of Permeability, Diapause, and Hatching in the Eggs of the Mosquito Aedes Hexodontus Dyar

Abstract

Methods for collection in the laboratory of many thousands of eggs from field-collected, blood-fed females are described. Also a way of separating fertile from infertile eggs is outlined. When the eggs are laid they are white but begin to darken within one-half hour. The darkening did not occur when the egg cell or early embryo was killed.Two changes in permeability in the prediapause stage of the eggs of Aedcs hexodontus were observed. The first took place as the chorion changed from white to black. The egg lost and gained water easily when first laid but resisted water loss and uptake as the chorion darkened. However, a complete waterproofing did not result. With the formation of the transparent cuticle a further change in permeability occurred. The egg lost hardly any water even when exposed to extreme desiccation and what little water was lost was regained very slowly. However, the cuticle, with the chorion removed in sodium hypochlorite, was quite permeable. The impermeability of the chorion and cuticle combination must result from the bonding between the two and this bonding must be disrupted by the dechorionation.To study the obligate diapause that occurs in the late embryogeny of the mosquito egg the effect of making water available to the embryo, of light, and of low temperature was studied. Diapause was not broken when water was available to the embryo, nor did alternate periods of light and dark at room temperature or at lower temperatures disrupt the diapause. To test the influence of cold the temperature of 1° and −3 °C. were used to simulate the temperatures in the field. The low temperatures were found to terminate the diapause but the numbers of eggs hatching did not steadily increase with an increase in the time of exposure to cold. No clue has as yet been discovered to explain these results. A hatching infusion of decaying adult mosquito bodies in distilled water was found to give more hatching than did distilled water alone. The mechanism of the hatching stimulus is not known.

A chitin-like component in Aedes aegypti eggshells, eggs and ovaries

“…X-ray diffraction studies (Harwood, 1958). Histochemical tests suggested that a chitin-like component is a component of the shell (Beckel, 1958), but the presence of chitin has never been confirmed by other techniques. In addition, there is no agreement about the tissue source of the chitin-like component; some authors suggested that it is of embryonic origin (Harwood and Horsfall, 1959;Clements, 1992), while others have indicated that it is synthesized by ovarian follicular epithelial cells (Powell et al, 1986).…”

“…It has been proposed that there is a chitin-like component present in mosquito eggshells (Beckel, 1958;Harwood and Horsfall, 1957;Harwood, 1958;Powell et al, 1986). There is no doubt that eggshells or egg coverings play an important role in the survival of mosquito species.…”

“…Not all of the researchers focusing on eggshells agree about the number of layers that form the A. aegypti shell. Some consider it as having two layers (Powell et al, 1986(Powell et al, , 1987, whereas others conclude that it has three layers (Beckel, 1958;Harwood, 1958;Clements, 1992). X-ray diffraction studies (Harwood, 1958).…”

Potential Community-Based Control by Use of Plastic Film to BlockAedes aegypti(L.) Egg Adhesion

“…We postulated that the few embryos that survive acquired enough water in hyaluronic acid to survive and hatch. Alternate mechanisms resulting in damage to embryogenesis would include decreased oxygen intake as a result of poorly developed aeropyles (Jones 1968, Mohinder 2001, as well as lack of a water-proofing wax layer that is part of the serosa cuticle (Beckel 1958, Christophers 1960, Clements 1996.…”

“…Desiccation of the embryo begins shortly after the serosa cuticle is synthesized (Lazzaro-Rezende et al 2008). The serosa cuticle develops during embryogenesis and becomes the third layer of the egg shell, just beneath the endochorion (Beckel 1958, Clements 1996. Failure of egg adhesion after oviposition can prevent cuticle formation.…”