Depending on the species, a female mosquito will lay her eggs either individually or in attached groups called rafts. The eggs may be placed directly on the surface of still water or along its edges, in tree holes, or other areas that are prone to flooding from rain, irrigation or overflow. In some species, eggs may hatch within a few days of being laid, but the exact amount of time depends on temperature. If eggs are laid out of water but in an area that is subject to intermittent flooding, the embryo may lay dormant for several years until the ideal hatching conditions are met. Mosquito eggs can become dormant if the water they were laid has dried and become active once water returns. This can also happen during the larval or adult stage.
Once the egg hatches, the larval stage begins. The larvae of most mosquito species hang suspended from the surface of the water. An air tube extending from the larva's posterior to the water surface allows the larva to breath. Larvae filter-feed on aquatic microorganisms that reside near the surface of the water. The larvae are very sensitive to light, shadows and other water disturbances so they have a defense mechanism that they will use when they become alarmed, quickly diving deeper into the water by swimming rapidly in a "S" motion. As they feed, larvae outgrow their exterior covering and form a new larger skin, shedding their old ones. The length of the larval stage ranges from 4 to 14 days, varying with species, water temperature, and food availability.
There are approximately 170 different species of mosquitoes in the United States. Of those, 50 are found in Colorado. Within the District that the Alamosa Mosquito Control serves, 12 species have been identified. Of these, 7 are commonly found during our summer months of operation.
Historically, the most common species found is the Culex tarsalis, which is also the primary carrier of the West Nile virus. The Alamosa Mosquito Control office is continually looking for any new species that can make their way up from the south and potentially carry diseases such as chikungunya, dengue fever, and eastern equine encephalitis (sleeping sickness).
The pupal stage is a resting, non-feeding stage of development. This is also the stage where the mosquito is changing into an adult. The pupal stage of a mosquito is similar to the metamorphosis seen when a caterpillar changes into an adult butterfly. Although this is a resting stage, the pupae are actually mobile. Like the larva, the pupa is also very sensitive to light, shadows and other water disturbances. Instead of using the "S" motion, the pupa has now developed a tail and will use a tumbling motion to escape into deeper water. The pupal stage lasts from 1 1/2 to 4 days. Aterwards, the pupa's skin splits along the back, allowing the newly formed adult to slowly emerge and rest on the water surface.
The male mosquito will usually emerge first and will linger near the breeding site, waiting for the females. Mating occurs quickly after emergence due to high adult mortality rates. As much as 30% of the adult population can die per day. The females compensate for this by laying large numbers of eggs to assure the continuation of the species. Male mosquitoes will live only 6 or 7 days on average, feeding primarily on plant nectars. Females with an adequate food supply can live up to 5 months, but the average female survives about 6 weeks. To nourish and develop her eggs, the female usually must take a blood meal in addition to plant nectars. She locates her victims by the carbon dioxide and other trace chemicals exhaled, and the temperature patterns they produce. Mosquitoes are highly sensitive to several chemicals including carbon dioxide, amino acids, and octenol. The average female mosquitoes flight range is normally between 1 and 10 miles, but some species can travel up to 40 miles before taking a blood meal. After each blood meal, the female will lay her eggs, completing the life cycle. It is possible for a female to lay eggs many different times.