The behavior of the female mosquito determines where they eggs are laid, and this behavior is quite constant for a given species. Eggs are white when first deposited, and darken after an hour or two.
Other species of Aedes, and all species of Psorophora, lay their eggs on moist ground where they remain until flooding occurs. In some cases, hatching occurs as soon as the eggs are flooded, and several generations may occur each year (multivoltine). This includes the Psorophora group, and Ae. vexans, Ae. canadensis, Ae. cinereus and Ae. sollicitans. These are the reflood species.
Most others must be subjected to cold-conditioning in order for hatching to occur, thus there is only one generation per year (univoltine). Examples are Ae. stimulans, Ae. aurifer, Ae. excrucians, Ae. fitchii and Ae. abserratus. These are known as spring brood mosquitoes. The eggs of the species that are deposited on the soil are able to survive for long periods of time, sometimes years or more, until such a time that they get flooded and are able to hatch.
In general, mosquito eggs fall into 3 distinct groups:
(A) Those that are laid singly on the water's surface. Eggs of the Anophelene mosquito. These are elongated and oval, usually pointed at one end, and are provided with a pair of lateral floats.
(B) Those that are glued together to form rafts, which float on the water. Eggs of the Culex, Culiseta, Coquillettidia and Uranotaenia mosquito. This raft, which may contain 200 or more eggs, remains afloat on the surface of the water until hatching occurs, usually within a few days.
(C) Those that are laid singly out of the water, on the soil. Eggs of the Orthopodomyia, Ae. triseriatus and Ae. atropalpus are laid on the sides of tree or rock holes, or in artificial containers (like tires) just above the water line, so that with a rise in the water the eggs hatch. These are known as container species.