Effects of sugars on the kinetics of drying and on the survival of partially dehydrated larvae of Anopheles mosquitoes

Abstract The ability to cryopreserve a stage of Anopheles mosquitoes would facilitate the development of strains incapable of transmitting malaria. Cryopreservation requires that the freezable water in cell systems be removed or rendered incapable of undergoing ice formation. The present study was concerned with the rate at which water is removed from lst instar larvae of Anopheles gambiae by air-drying, with the extent of dehydration that the larvae will tolerate, and with the effect of trehalose and sucrose on both drying kinetics and survival. Eighty-one percent of the larvae are water. Air-drying removes 90% of that water in ~20 min. Survivals after partial dehydration are highest if the larvae are rehydrated in 1/2× isotonic saline (0.13 osm); they are poorest if rehydrated in water or 0.13 osm sucrose. In the former, about 34% survive the removal of half the water, but next to none survive the loss of >70% initial water. Prior exposure to 0.2 M trehalose for as little as 1 min slows the drying rate and increases the tolerance of the larvae to dehydration. With 30-min exposure, 88% survive the loss of 50% of their water and 63% survive the loss of 75%. Protection is abolished with 0.4 M trehalose. The results are similar with sucrose. It is substantially reduced if sugar-exposed larvae are briefly washed with water prior to drying. The protection appears not to be related to the decreased drying rate. Rather it appears related, by an unknown mechanism, to the presence of sugar on the outer surface of the larvae.