There are over 3,000 different species of mosquitoes throughout the world; currently 176 species are recognized in the United States, 80 species of mosquitoes have been found in Florida, and more than 45 species have been identified in Pasco County. Many mosquito species have a different habitat, behavior and preferred source of blood. Organized mosquito control is necessary because mosquitoes are not only a nuisance as biting insects, but are also involved periodically in transmitting diseases to humans and animals.
All mosquitoes have four stages of development – egg, larva, pupa, and adult. While some mosquitoes lay their eggs on the surface of the water, the most abundant species deposit their eggs on moist soil. These eggs can overwinter and may lie dormant for several months and even years not hatching until they are covered by rain water or tides. Four to five days after the eggs hatch, the larvae are full grown. By this time, they have changed their shape, become less active, and enter into their pupae stage. After one to two days, the pupal skin splits at the water’s surface, and the adults emerge and are soon ready to bite.
When an adult mosquito emerges from the pupa they mate, and the female seeks a blood meal to obtain the protein necessary for the development of her eggs. With one blood meal, a female may produce as many as 250 or more eggs. After a blood meal, it takes 3-5 days for blood to be digested and the eggs to develop.
The male mosquito does not take a blood meal but may feed on plant nectar. He lives for only a short time after mating, while the female can live for over two weeks, producing 2-4 egg batches. Females transmit diseases when they live long enough to spread pathogens from the first blood meal victim to the second blood meal victim. Only a very small percentage of mosquitoes live this long.
A Culex raft containing 200-250 individual eggs. This stage lasts 1-2 days, and then larvae emerge
Culex larvae (wigglers) develop as four instars in 5-10 days, and then they become pupae (tumblers).
Culex pupae metamorphose over 1-2 summer days into adults. They do not eat during this period.
Females seek a place to lay their eggs, and the site chosen is probably based on clues from chemical receptors on their body. Mosquitoes have two general egg laying (oviposition) strategies which are usually specific for each species. Mosquitoes will either lay eggs on existing water bodies, or they will lay eggs at sites that will later be flooded. In either case, the egg requires 1-2 days of water before the 1st instar larvae are released. The female mosquito stores the sperm she received through mating, and eggs are fertilized at the time they are laid. The development time of the egg is about 1-2 days, and during this period the egg turns from white to black as its outer shell hardens to protect it from a hostile environment.
Once the eggs hatch, the larvae begin eating voraciously, and they grow rapidly, from about 1/16-inch to nearly 3/8-inch or greater in size. Mosquito larvae eat microscopic plants (algae) and animals (phytoplankton) by filter feeding and grazing. Mosquitoes (and other invertebrates) do not have an internal skeleton like we do to support their organ systems. Instead, they have a hard external skeleton (exoskeleton) made of chitin. This hard exoskeleton hinders their rapid growth, and they shed it four times during the larval stage. Each one of the sub-stages in mosquito larval development is called an “instar”. This development process usually takes about 4-10 days in summer months, depending on the species and ambient temperature. However, some mosquitoes spend the winter in the water as 3rd instar larvae, and hatch off together in great hordes in spring as water temperatures rise. Those mosquito species that lay their eggs in areas that later are flooded with tides or rainwater also tend to have vast synchronous broods, whose peak population numbers are low during subsequent development times. In contrast, those species that lay their eggs on the water surface tend to have a more constant population numbers (usually too many for our comfort) if the environmental conditions are stable.
The next stage is the pupa, or tumbler. This stage usually lasts about 2 days. During this time the mosquito transforms from the aquatic larva into the flying adult. The pupa does not feed. If you look carefully at a pupa through its semi-transparent exoskeleton, you will see the developing adult inside. After a suitable development time, the adult emerges from the exoskeleton at the water surface, dries its wings, and takes flight to begin the cycle again.
The mosquito must breathe air to live. In both the larval and the pupal stage, the mosquito takes advantage of the surface tension of the water to stay attached to the surface layer so that they may gather air through special appendages called “siphons” for larvae and “horns” for pupae. Adults also use the water surface tension to stay suspended when they are emerging from pupal cases, drying their wings, and/or landing and laying their eggs.