Mosquitoes: Designed by God to make flies seem better - Ivan Itch Mosquito
Mosquitoes have complete metamorphosis. Their life cycle consists of four stages: egg, larva, pupa and adult. They may lay the eggs singly or in rafts on water, on the sides of containers where water will soon cover, or on damp soil where they can hatch by rainwater or high tides.
No matter what the mosquito species, water is essential for breeding. The larval stage is aquatic and mosquito larval habitats are many and varied. Mosquito larvae prefer still water and can be found in water holding containers, tree holes, roadside ditches, low lying areas, swamps, and tidal salt marshes. Mosquitoes are not found in moving streams and rivers or in areas subjected to heavy wave action. Since much of the Coastal Plain of Maryland is subjected to flooding, mosquitoes breed in urban and suburban areas of Maryland and on the Eastern Shore. Contrary to popular belief, mosquitoes do not breed in tall grass or thick brush. These areas provide an excellent refuge for adult mosquitoes during the heat of the day but in no way contribute to mosquito breeding, nor do they provide habitat for mosquito larvae.
Mosquito eggs are usually elongated, about one millimeter long and they lay them in batches of 50-300. One female may lay several batches. A blood meal provides the proteins necessary for egg development. Eggs can hatch in one to three days if laid on warm water. Other species lay eggs in containers or on the soil that may flood and require a longer drying period before hatching. Eggs of these floodwater mosquitoes have evolved to have incremental hatching, that is, all eggs do not hatch together. Instead, about 80% of the eggs hatch during the first flooding, with 5% hatching following subsequent flooding. Many species lay eggs that remain dormant in the soil for years before hatching. This adaptation insures mosquito survival despite unfavorable weather conditions and/or human efforts to eradicate them.
The larva lives in water but breathes air through a siphon that penetrates the water surface, or, in some species pierces the roots of aquatic plants such as cattails. Mosquito larvae feed on microorganisms and organic particles using mouthparts modified into "brushes" which draw food into the mouth. During the larval stage four separate developmental periods occur called instars. As a mosquito larva grows, it must "cast off" its exoskeleton and replace it with a larger one. Therefore, passage from one instar period to the next results in a larva that grows gradually larger. A larva changes into a pupa in about a week.
Mosquitoes remain in the pupal stage for one to two days. During this period, the mosquito changes its life form (metamorphosis) from a larva that lives in water, to a flying adult that lives in a terrestrial environment. Male mosquitoes emerge from the pupa first and rest near the breeding site. They feed on nectar (a carbohydrate source) from flowers. Female mosquitoes feed on nectar and blood. Blood is necessary for egg development following mating. Without blood mosquitoes cannot produce eggs. In fact, mosquitoes select specific hosts from which to blood feed. Some mosquitoes feed only on mammals, others only on birds and some may blood feed on both these warm-blooded creatures. In some parts of the globe, some mosquito species feed principally on humans. This is especially true of many species that transmit malaria in the tropics. Other mosquitoes prefer cold-blooded animals such as amphibians (frogs etc.) or reptiles (turtles and snakes etc.).
In Maryland, we have two species that live in the carnivorous pitcher-plant as larvae. They feed on the remains of the plant's prey but are unaffected by its digestive enzymes. Some mosquito species are predatory and feed on other mosquitoes during the larval stage. We rear these species as part of our program to control mosquitoes breeding in containers or tree holes.
Most mosquitoes are active at dusk or at night (nocturnal). Others prefer the day for their peak period of activity. Another interesting fact is that many mosquitoes seek a host according to altitude and distance from a breeding site. They partition feeding habits. For instance, salt marsh mosquitoes feed on hosts within 3 meters of the ground. Tree hole species feed at heights of up to 30 meters or more, seeking vulnerable nestling birds as the source of their blood meal. Some mosquitoes have a home range of less than one kilometer while the salt marsh species that live along the Chesapeake Bay and Atlantic Coast marshes fly up to 40 kilometers to find a host.
E-Mail Jeannine Dorothy, Maryland Department of Agriculture Mosquito Control
