Zika Series: The Life Cycle of Aedes Mosquitoes

The life cycle of Aedes species mosquitoes if fairly short. Aedes aegypti lay their eggs on a damp surface near water, while Aedes albopictus prefers to lay them on a dry wall above the water and wait for rain to raise the water level to submerge the eggs. They lay up to 200 eggs each time they oviposit and can oviposit as often as once every week. Mosquito eggs are very resilient; if their water source dries up before the eggs hatch they can stay viable on the dry ground for months, waiting for the next large rainfall or flood to provide the right environment.

After 2-7 days near the water the eggs hatch into larvae. The larvae feed on the microorganisms living in the water with them, such as bacteria and fungi. As the larvae grow they will alternate between instars (feeding periods) and molting. Aedes mosquito larvae go through 4 instars. Once the 4th instar is completed the larva will turn into a pupa. This may take 6-8 days depending on the environmental conditions.

The pupal case is where the adult mosquito is formed. The larvae may grow to 8 mm in length, but most of that will be converted back into energy to help it transition into an adult mosquito. The pupa does not feed, but instead floats near the water surface. If the pupa detects threatening stimuli it will dive deeper into the water to hide. The development of an adult mosquito in a pupal case takes 2-3 days.

Adult mosquitoes primarily feed on flower nectar or other sugary liquids. Only the females bite humans to obtain the protein necessary to develop more eggs. Both Aedes aegypti and Aedes albopictus are estimated to have a flight range of 200 meters. They tend to feed early in the morning and early in the evening.

A mosquito that carries a disease-causing agent like the Zika virus is called a vector. The virus is typically transmitted to or from the mosquito when it obtains a blood meal from a human. However, the mosquitoes are also happy to feed on other mammals like cattle or household pets. These animals are safe from infection, but the blood meal may still enable the mosquito to produce more eggs, which will lead to more potential disease vectors in future generations. Aedes aegypti has shown a preference for human hosts over other mammals, and may feed on multiple hosts in a single gonotrophic cycle, increasing the risk of disease transmission.

An Aedes mosquito will take roughly 14 days to complete a full life cycle from hatching to ovipositing its first batch of eggs. Adult Aedes mosquitoes live for around 40 days. In this life cycle a female Aedes aegypti mosquito may lay up to 5 batches of eggs, resulting in up to 1000 new potential disease vectors. The females tend to live longer than males and their life span may be extended for several months in humid climates.

Host-Seeking Behavior

Like most insects, the central nervous system of a mosquito is simple. Innate behaviors are triggered by external and internal stimuli. This includes host-seeking behavior, which may begin less than 24 hours after emerging from the pupa. When seeking a host, mosquitoes follow trails of chemicals given off by people. They “see” people as plumes of rising carbon dioxide, but they also follow other chemicals like lactic acid, ammonia and octenol.

Pre-Oviposition Behavior

Once the mosquito has found enough hosts to feed and develop its eggs, it is time to locate a suitable oviposition site. Aedes albopictus prefers naturally occurring sites like tree holes, but Aedes aegypti is usually found in artificial containers. This includes discarded tires, flowerpots, rainwater barrels, buckets, standing water in shower drains and toilet tanks, just to name some. The mosquitoes tend towards darkly colored water vessels, following a concentration gradient of water vapor. Because the larvae are dependent on the vessel’s microbial flora for nutrition, chemicals associated with bacterial cultures are very attractive at this stage of the mosquito life cycle. We will discuss these more in future posts.

Even Skjervold
Program Manager for Biomedical Engineering
Eagle Medical Services, LLC

3 thoughts on “Zika Series: The Life Cycle of Aedes Mosquitoes

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