Survival of Aedes vittatus (Diptera: Culicidae) eggs in hot, dry rockpools

When granite rockpools are artificially flooded during the long (4-5 months) dry season, Aedes vittatus larvae appear. The source of these, whether from gravid females or from eggs surviving in a desiccated state, was tested for by sealing 8 rockpools with plastic mesh screening after the last rains. Two pools yielded Ae. vittatus and Ae. aegypti larvae after the first rain 4.5 months later, during which dry season soil temperatures reached 40 degrees C and air relative humidity fell as low as 5%. A laboratory experiment showed that Ae. vittatus did not oviposit through plastic mesh screening and therefore the larvae which appeared were from eggs present before the pools were screened. Known numbers of Ae. vittatus eggs laid on damp mud were placed in dry rockpools for 10 weeks and kept dry for a further 6 weeks in the laboratory. This resulted in a 7% hatch rate compared to 44% in the laboratory control and 79% in freshly laid eggs. It is concluded that the survival of Ae. vittatus eggs over the dry season is sufficient to lead to a rapid population explosion when the rains start.