Permeability of intact and dechorionated eggs of the Anopheles mosquito to water vapor and liquid water: a comparison with Drosophila.

As an initial step in the development of cryopreservation methods for Anopheles gambiae embryos, we determined the permeability of intact and dechorionated A. gambiae embryos to water and ethylene glycol and compared those permeabilities with those of Drosophila melanogaster embryos. Most studies were conducted on embryos allowed to develop for 8 h at 26 degrees C or 15 h at 17 degrees C. Intact A. gambiae embryos are some 50 times more permeable to water vapor than are D. melanogaster embryos; e.g., when air dried, half of 15 h/17 degrees C A. gambiae embryos become severely dehydrated in 3. 5-4.0 min, whereas comparably aged D. melanogaster embryos require approximately 4 h or more. Comparable differences between the two species exist with respect to the loss of liquid water under an osmotic driving force. After 90 min in 0.75 M sucrose in 0.26 osmolal D-20 Drosophila medium, 25-40% of intact A. gambiae embryos underwent extensive shrinkage, whereas D. melanogaster embryos showed no shrinkage. The chorion of both species can be removed by a 2.5-min exposure to 50% household bleach (Clorox). Dechorionation increases the rate of water loss two- to sixfold during air drying in both species and during exposure to hyperosmotic sucrose in A. gambiae. Dechorionated D. melanogaster embryos, however, show no shrinkage in hyperosmotic sucrose even after 6 h. The water permeability of dechorionated A. gambiae embryos thus remains many-fold higher than that of dechorionated D. melanogaster embryos. Although moderately permeable to water, neither intact nor dechorionated A. gambiae embryos are permeable to ethylene glycol, as evidenced by the failure of dehydrated embryos to reexpand in 120-180 min in that solution.