What is the life cycle of mosquitoes?
Mosquitoes of different species lay their eggs in a variety of water sources that range from small containers to vast expanses of marshland. The larval stage is always aquatic and shuttles from the subsurface where it filter feeds on micro-organisms to the surface to obtain oxygen through a snorkel-like breathing apparatus. The pupal stage does not feed but unlike most insect pupae is extremely active. The adult emerges from the pupal case using air pressure and assume a terrestrial existence.
Mosquitoes have four stages of development: egg, larva, pupa and adult. As mentioned, they spend their larval and pupal stages in water. Female mosquitoes of most pest species in Mercer County deposit eggs on moist surfaces such as mud or fallen leaves. Rain refloods these surfaces and stimulates the hatching of the eggs, thus starting the life cycle. Other mosquito species in the county lay their eggs on the surface of permanent water and since the water is constantly present, there are always eggs hatching and larvae developing.
Mosquitoes take approximately one week to develop from egg to the flying adult. After emerging from the aquatic stages, adult mosquitoes mate and the females seek a blood meal to obtain nutrients necessary for egg development. Only the female adult bites, while both sexes utilize sugar sources for general nutrient requirements. While various species differ significantly, the average life expectancy for adult mosquitoes is 4-6 weeks during the summer.
How many kinds of mosquitoes are there?
About 3000 species of mosquitoes have been described on a world-wide basis with approximately 150 known to occur in North America. The term "Mosquito State" is appropriate for New Jersey because 63 species of mosquitoes have been found within its boundaries, to date. Only 15 of those species have been documented in Mercer County so far. This number should rise drastically, as the surveillance and identification efforts of the county improve for the upcoming season.
Why do mosquitoes bite?
Mosquitoes belong to a group of insects that require blood to develop fertile eggs. Males do not lay eggs, thus, male mosquitoes do not bite. The females are the egg producers and "host-seek" for a blood meal. Female mosquitoes lay multiple batches of eggs and require a blood meal for every batch they lay. Few people realize that mosquitoes rely on sugar as their main source of energy. Both male and female mosquitoes feed on plant nectar, fruit juices and liquids that ooze from plants. The sugar is burned as fuel for flight and is replenished on a daily basis. Blood is reserved for egg production and is imbibed less frequently.
Why do mosquitoes leave welts when they bite?
When a female mosquito pierces the skin with her mouthparts, she injects a small amount of saliva into the wound before drawing blood. The saliva makes penetration easier and prevents the blood from clotting in the narrow channel of her food canal. The welts that appear after the mosquito leaves is not a reaction to the wound but an allergic reaction to the saliva injected to prevent clotting. In most cases, the itching sensation and swellings subside within several hours. Some people are highly sensitive and symptoms persist for several days. Scratching the bites can result in infection if bacteria from the fingernails are introduced to the wounds.
Can mosquitoes carry diseases?
Any insect that feeds on blood has the potential of transmitting disease organisms from animal to human. Mosquitoes are highly developed blood-sucking insects and are the most formidable transmitters of disease in the animal kingdom. Mosquito-borne diseases are caused by human parasites that have a stage in their life cycle that enters the blood stream. The female mosquito picks up the blood stage of the parasite when she imbibes blood to develop her eggs. The parasites generally use the mosquito to complete a portion of their own life cycle and either multiply, change in form inside the mosquito or do both. After the mosquito lays her eggs, she seeks a second blood meal and transmits the fully developed parasites to the next unwitting host. Malaria is a parasitic protozoan that infects the blood cells of humans and is transmitted from one human to the next by Anopheles mosquitoes. Encephalitis is a virus of the central nervous system that is passed from infected birds to humans by mosquitoes that accept birds as blood meal hosts in addition to humans. Yellow fever is a virus infection of monkeys that can either be transmitted from monkey to human or from human to human in tropical areas of the world. Dog heartworm is a large filarial worm that lives in the heart of dogs but produces a blood stage small enough to develop in a mosquito. The dog heartworm parasite does not develop properly in humans and is not regarded as a human health problem. A closely related parasite, however, produces human elephantiasis in some tropical areas of the world, a debilitating mosquito-borne affliction that results in grossly swollen arms legs and genitals.
Can mosquitoes transmit AIDS?
The HIV virus that produces AIDS in humans does not develop in mosquitoes. If HIV infected blood is taken up by a mosquito the virus is treated like food and digested along with the blood meal. If the mosquito takes a partial blood meal from an HIV positive person and resumes feeding on a non-infected individual, insufficient particles are transferred to initiate a new infection. If a fully engorged mosquito with HIV positive blood is squashed on the skin, there would be insufficient transfer of virus to produce infection. The virus diseases that use insects as agents of transfer produce tremendously high levels of parasites in the blood. The levels of HIV that circulate in human blood are so low that it is unlikely for a mosquito to pick up any sufficient numbers for a secondary infection.
For more information on mosquitoes and mosquito-borne diseases, please visit the following sites:
- New Jersey Mosquito Biology and Control- www.njmosquito.org
- American Mosquito Control Association- www.mosquito.org
What can homeowners do?
Homeowners can provide effective control by eliminating standing water on their property. Any container holding water is a potential mosquito-breeding source and is likely to cause problems around the house. Of particular concern are clogged gutters and scattered tires. Both tend to collect leaves, then fill with water and provide very attractive sites for mosquitoes to breed. Since these containers are water tight, they dry out very slowly and are generally the cause of mosquito problems around the home. Gutters should be kept clean and other containers removed or overturned to limit mosquito-breeding sites. Items such as dog water bowls, horse-watering troughs, and birdbaths should be emptied and refilled at least once a week.
Small depressions in the yard can be filled to prevent the accumulation of water. If larger wet areas exist on the property, they should be brought to the attention of the MCMC.
Keeping adult mosquitoes out of the home is another step. Homeowners should make sure that window and door screens are properly fitted and holes patched to prevent mosquitoes from entering the home.
Personal protective measures should also be undertaken to limit exposure to mosquitoes as much as possible. Limit outdoor activities during the dawn and dusk hours when most species of mosquitoes are active. If outdoor activity is necessary, wear long sleeve clothing to limit exposure areas to mosquitoes. A wide variety of repellents are available to provide relief from mosquitoes and other biting insects. Most repellents contain the same active ingredient, and are readily available at a variety of stores. Repellents are generally effective but caution should be used and manufacturers directions followed carefully.