Mosquitoes

Mosquitoes are vectors that carry disease-causing viruses and parasites from person to person without exhibiting symptoms themselves

The principal mosquito-borne diseases are the viral diseases yellow fever, dengue fever and Chikungunya transmitted mostly by the Aedes aegypti and malaria carried by the genus Anopheles spp

Mosquitoes serve as vectors of important diseases, such as the West Nile virus, filariasis, Japanese encephalitis, St. Louis encephalitis and avian malaria

Dengue is transmitted by several species of mosquito within theAedes genus, principally Aedes aegypti

The Dengue virus has four different types; infection with one type usually gives lifelong immunity to that type, but only short-term immunity to the others

Subsequent infection of dengue with a different type is believed to increase the risk of severe complications

Malaria is transmitted by the female Anopheles to humans and is caused by eukaryotic protists of the genus Plasmodium

Four species of Plasmodium can infect and be transmitted by humans

Most dangerous form of malaria is also caused by Plasmodium falciparum

Malaria is also caused by Plasmodium vivax, Plasmodium ovate andPlasmodium malariae, which is generally a milder disease that is rarely fatal

Like all insects, adult mosquitoes have three basic body parts:

• Head - This is where all the sensors are, along with the biting apparatus. The head has two compound eyes, antennae to sense chemicals and the mouth parts called the palpus and the proboscis (only females have the proboscis, for biting)
• Thorax - This segment is where the two pair wings and six legs are attached. It contains the flight muscles, compound heart, some nerve cell ganglia and trachioles
• Abdomen - This segment contains the digestive and excretory organs

• Mosquitoes are like flies in that they have two pairs of wings, but unlike flies,their wings have scales
• Their legs are long and the females have a long mouth part (proboscis) for piercing skin
• Mosquitoes have a battery of sensors designed to track their prey, including:
• Chemical sensors - mosquitoes can sense carbon dioxide and lactic acid up to 100 feet (36 meters) away. Mammals and birds gives off these gases as part of their normal breathing.Certain chemicals in sweat also seem to attract mosquitoes
• Visual sensors - if you are wearing clothing that contrasts with the background, and especially if you move while wearing that clothing, mosquitoes can see you and zero in on you
• Heat sensors - Mosquitoes can detect heat, so they can find warm-blooded mammals and birds very easily once they get close enough

• Mosquitoes are members of the order diptera and undergo complete metamorphosis. The four stages are: Egg, Larva, Pupa, Adult
• You can distinguish the larvae of various mosquito species. Anopheles larvae lie parallel to the surface of the water, while larvae of Aedes and Culex extend down into the water (the air tubes of Culex are longer than those of Aedes). Some mosquitoes, such as the cattail mosquito (Coquilettidia perturbans), are becoming more prevalent pests as humans invade their habitats
• Like all insects, mosquitoes hatch from eggs and go through several stages in their life cycle before becoming adults. The females lay their eggs in water, and the larva and pupa stages live entirely in water. When the pupa change into adults, they leave the water and become free-flying land insects. The life cycle of a mosquito can vary from one to several weeks depending upon the species

Egg - All mosquitoes lay eggs in water,which can include large bodies of water, standing water or areas of collected standing water (like tree holes or gutters). Females lay their eggs on the surface of the water, except for Aedes mosqui­ toes, which lay their eggs above water in protected areas that eventually flood. The eggs can be laid singly or as a group that forms a floating raft of mosquito eggs

Larva - The mosquito eggs hatch into larvae or "wigglers," which live at the surface of the water and breathe through an air tube or siphon. The larvae filter organic material through their mouth parts and grow to about 1 to 2 em long; as they grow, they shed their skin (moult) several times

Pupa - After the fourth moult, mosquito larvae change into pupae or "tum­ blers," which live in the water anywhere from one to four days depending on the water temperature and species . The pupae float at the surface and breathe through two small tubes (trumpets)

Adult - Inside the pupal case, the pupa transforms into an adult. The adult uses air pressure to break the pupal case open, crawls to a protected area and rests while its external skeleton hardens, spreading its wings out to dry. Once this is complete, it can fly away and live on land

Male mosquitoes have short mouth parts and feed on plant nectar. In contrast, female mosquitoes have a long proboscis that they use to bite animals and humans and feed on their blood (the blood provides proteins that the females need to lay eggs). After they feed, females lay their eggs (they need a blood meal each time they lay eggs). Females continue this cycle and live anywhere from many days to weeks (longer over the winter). Males usually live only a few days after mating.

Aedes

• These are sometimes called "floodwater" mosquitoes because flooding is important for their eggs to hatch
• Aedes mosquitoes have abdomens with pointed tips
• They include such species as the yellow-fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus)
• They are strong fliers, capable of travelling great distances (up to 75 miles/121 km) from their breeding sites
• They persistently bite mammals (especially humans), mainly at dawn and in the early evening
• Their bites are painful

Anopheles

• These tend to breed in bodies of permanent fresh water
• Anopheles mosquitoes also have abdomens with pointed tips
• They include several species, such as the common malaria mosquito (Anopheles quadrimaculatus), that can spread malaria to humans
• When resting, the stomach area of Anopheles mosquito points upwards

Culex

• These tend to breed in quiet, standing water
• Culex mosquitoes have abdomens with blunt tips
• They include several species such as the northern house mosquito (Culex quinquefasciatus)
• They are weak fliers and tend to live for only a few weeks during the summer months
• They persistently bite (preferring birds over humans) and attack at dawn or after dusk
• Their bite is painful

• As there are no vaccines for malaria and dengue, prevention is sought by reducing the habitat and the number of mosquitoes and limiting the exposure to bites
• Space spraying and indoor residual spraying with a long lasting insecticide
• Larvicides may be used to control mosquito larvae