Mosquitoes

More than 3000 species of mosquitoes have been described on a world-wide basis. Scientists group species by genus on the basis of the physical characteristics they share. The 3000 mosquito species found in the world are divided among 28 different genera. The genus Aedes contains some of the worst pests. Many members of the genus Anopheles have the ability to transmit human malaria.

There are three genera of medical importance: Culex Aedes Anopheles

Morphology 1. Body: small, fragile, 3-6mm long 2. Distinguishing of sexes: 1) Antenna: plumose in male, pilose in female 2) Palp 3) External genitalia 3. Mouthparts, piercing and sucking type. Proboscis and 6 needles.

Egg Elongate elipsoid, about ½ mm. Anopheles egg, The eggs have distinct lateral floats.

Anopheles sp egg with tuberculated surface and a distinct float in the center. Anopheles eggs, with a larva emerging. The eggs have distinct lateral floats which easily differentiates them from culicine eggs.

Culcine eggs are laid in rafts.

Aedes Egg Laid singly in or near water.

Larva (wigglers) A newly emerged anopheles (1st instar larva).

Pupa Like a “,” divided into cephalothorax and abdomen. It moves actively but takes no more food.

Morphological difference of three genera

Anopheles Culex Aedes

Anopheles Culex Aedes Anopheles Culex Aedes

Anopheles

Culex

Aedes

Life Cycle of a Mosquito 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.

Holometabola Egg — 1-4 days-> larva (4 stages)— 7 days -> pupa – 2-3 days  adult days total.

Habit or Bionomics

Eggs: Larvae (wigglers or wrigglers): Pupae: Adults:

Larval Habitats of Mosquitoes Mosquito larvae can be found in numerous habitats. Each habitat produces specific mosquito species. Habitats can be generally grouped into four types: Running Water, Transient Water, Permanent Water, or Container.

Running Water Few mosquito species breed in running waters, such as streams. Larvae can be flushed out when stream volume increases, and to remain in the stream requires a large amount of energy.

Transient Water Transient water sources, such as flooded areas, snowpools, and ditches are used as breeding grounds for mosquito species whose eggs can withstand desiccation, such as Aedes.

Transient waters include: Woodland Pools - (Snowpool )

Woodland Pools -(Spring Rains)

Fresh Floodwater

Tidal Floodwater

Permanent water These waters (also known as Semi- permanent) are present for extended periods of time and support characteristic aquatic vegetation. Cattail, rushes and sedges are typical freshwater swamp vegetation. Genera associated with permanent water are Anopheles, Culex, and so on.

Containers Container water habitat can be found in both natural settings, such as water held by plants (bromeliads) to artificial settings, such as water found in tires. The habitat of containers are based on the containers themselves. Treehole sites generally have tannin-enriched water which is characteristically clear, with rotting wood at the bottom. Many treehole species now also use artificial sites, such as tires since they provide insulation against the weather and are more numerous. Artificial containers are a convenient mode of transporting a species of mosquito outside of it's natural range.

Adult 1. Breeding places: 2. Hiding and resting places: dark, poorly ventilated and humid places.

3. Feeding: Mosquitoes belong to a group of insects that requires 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.

3. Feeding: Finding host: By sight (movement) Detecting infrared radiation Chemical signals: CO 2, lactic acid, etc.

Why are some people more attractive to mosquitoes than others? Scientists are still investigating the complexities involved with mosquito host acceptance and rejection. Some people are highly attractive to mosquitoes and others are rarely bothered. Mosquitoes have specific requirements to satisfy and process many different factors before they feed. Many of the mosquito's physiological demands are poorly understood and many of the processes they use to evaluate potential blood meal hosts remain a mystery. Female mosquitoes use the CO 2 we exhale as their primary cue to our location.

A host seeking mosquito is guided to our skin by following the slip stream of CO 2 that exudes from our breath. Once they have landed, they rely on a number of short range attractants to determine if we are an acceptable blood meal host. Folic acid is one chemical that appears to be particularly important. Fragrances from hair sprays, perfumes, deodorants and soap can cover these chemical cues. They can also function to either enhance or repel the host seeking drive.

Dark colors capture heat and make most people more attractive to mosquitoes. Light colors refract heat and are generally less attractive. Detergents, fabric softeners, perfumes and body odor can counteract the effects of color. In most cases, only the mosquito knows why one person is more attractive than another.

4. Seasonal Distribution: Above 10 o C, mosquitoes will move from their hiding places and become active. In Shandong they are prevalent from May to October.

5. Hibernation: Mosquitoes, like all insects, are cold blooded creatures. As a result, they are incapable of regulating body heat and their temperature is essentially the same as their surroundings. In tropical areas, mosquitoes are active year round. In temperate climates, adult mosquitoes become inactive with the onset of cool weather and enter hibernation to live through the winter. Some kinds of mosquitoes have winter hardy eggs and hibernate as embryos in eggs laid by the last generation of females in late summer. The eggs are usually submerged under ice and hatch in spring when water temperatures rise.

Other kinds of mosquitoes overwinter as adult females that mate in the fall, enter hibernation in animal burrows, hollow logs or basements and pass the winter in a state of torpor. In spring, the females emerge from hibernation, blood feed and lay the eggs that produce the next generation of adults. A limited number of mosquitoes overwinter in the larval stage, often buried in the mud of freshwater swamps. When temperatures rise in spring, these mosquitoes begin feeding, complete their immature growth and eventually emerge as adults to continue their kind.

6. Life span: Males, 1-3 weeks. Females, much longer. Hibernating females may live as long as 5 months or more. 7. Range of flight: 500 meters long and 300 meters high.

Mosquitoes and diseases 1. Annoyance pest: A mosquito bite may induce local dermatitis or even systematic reaction in sensitive persons.

Child with hypersensitivity to mosquito bites. Mosquito bites can produce a severe allergic reaction. In this case the child displayed both the immediate and the delayed type reactions. The scars on the forearms are due to necrotic changes which occurred during the delayed type reaction.

2. Parasitic diseases: Malaria and filariasis. 3. Virus diseases: Japanese encephalitis B, mainly by Aedes and Culex tritaeniorrhyncus. Dengue fever and yellow fever. 4. Mechanical transmitter: Some mosquitoes may carry fly eggs to humans, inducing myiasis.

Can mosquitoes transmit AIDS?

Control 1. Individual protection by site selection for homes, nets or screens, chemical repellents, etc. 2. Elimination of breeding places. 3. Insecticides. 4. Biological: Genetic control and protection of mosquitoes’natural enemies (bat, dragon fly, swallow, Gambusia fish, etc.)