Back to: O level Biology NOTES Uganda syllabus

The mosquitoes are majorly found in the tropics and are best known for carrying disease germs

They belong to the order Diptera and the important three genera are:

  1. Anopheles that are vectors of malaria
  2. Culex which are vectors of dengue fever and
  3. Aedes, the vector of elephantiasis and yellow fever

Classification

Kingdom : Animalia

Phylum : Arthropoda

Class : Insecta

Order : Diptera

Family : Culicidae

Genus : Anopheles

Species : Anopheles, Aedes and Culex

Structure of mosquito

Mosquitoes are slender, long-legged insects and like all other Dipterans, they have proboscis, a pair of wings and a pair of halteres. Male mouth parts are for sucking but the female mouth parts are for piercing and sucking.When the female mosquito bites someone, she pierces the skin with the stylets and inserts the sucking and salivary tubes. Saliva is secreted into the wound and prevents the blood from clotting and blocking the tubes mean while the labium bends back.

THE MOSQUITO

Features on the thorax

  • The thorax is large and easily visible.
  • It has the usual three segments bearing a pair of long slender legs.
  • The mesothorax bears a pair of membranous, transparent wings while the metathorax bears a pair of halteres used in balancing and also sensory in function.
  • Has a pair of spiracles on each segment.

Features on the abdomen

  • The abdomen is long and slender.
  • It has 10 segments but only 8 are seen.
  • It has a pair of spiracles on each segment.
  • The last segment bears the external genitalia

Mode of life of a mosquito

  • Hates light and like resting in dark places during day and comes out to feed at night
  • They feed mainly within late evening and early morning (day and dawn)
  • Male mosquitoes feed on plant juices and nectar while the female feed on blood.

Life cycle of a Mosquito

It begins with mating and internal fertilization and is a complete metamorphosis. The difference however are observed for both Anopheles and Culex mosquitoes Mosquitoes eggs are laid in still water (swampy pools, water collected in old pots/ tins, in axils of leaves, blocked drains or gutters), and the earliest stages of life take place in water.The eggs are boat shaped and those of Culex species stick together to form raft. Those of anopheles are laid singly each with air float.

The larva consists of a head, thorax and abdomen. It swims through water, tail first by wriggling its abdomen. Culex larva uses Siphons for obtaining oxygen whereas an anopheles uses spiracles, located on the eighth abdominal segment on both types of lava.

The pupa differs from the larva in being fairly active. It is comma-shaped with two tail fins at the end of the abdomen. It breathes atmospheric oxygen through a pair of trumpets on the thorax.After few days the pupa skin splits and adult emerges. It rests on pupa case while the wings unfold and harden and then flies a way.

THE MOSQUITO

Economic importance of mosquitoes

They carry malarial parasites which cause malaria. These germs are carried by a female anopheles. The disease causing parasite is referred to as plasmodium. The four types of plasmodia are;

  1. Plasmodium malariae
  2. Plasmodium vivax
  3. Plasmodium ovale
  4. Plasmodium falciparum

Symptoms of malaria

  • A Person with malaria has very high fever.
  • Headaches.
  • Sometimes vomiting.
  • Pain in the joints and sometimes the general body.
  • There is alternate cold and shivering spells as well as hot sweating.
  • Loss of appetite.Anemia.Enlarged liver and spleen.

Malaria may cause convulsions and sometimes death in children and abortions in pregnant women due to destruction of red blood cells by the parasites.

Control of spread of malaria

Of these diseases malaria is probably becoming the most serious and is increasingly becoming a killer of such great as AIDS. This is mainly because the parasites causing it are becoming resistant to drugs like chloroquine whichin the past have been very effective at old malaria.As things stand now, effective control of the mosquito is as much prerequisite to control malaria as it is to combat the disease.

Appropriate measures include;

  • Destroying the breeding places where larvae develop from by draining or applying a film of oil over the water surface to prevent oxygen reaching the mosquito larva.
  • Burning or burying all empty containers to prevent water from collecting during the rainy season.
  • Clearing bushes around homestead. Mosquitoes like to rest and breed on them during the rainy season.
  • Biological control which involves the introduction of fish into water bodies which feed on the larvae and pupa.
  • Mosquitoes can be killed by spraying with insecticides using special sprayers.
  • Removal of small water containers such as old tins, bottles, and drainage channels, so as to reduce on breeding sites.
  • protecting our bodies from mosquito bites by using mosquito nets at night as well as wearing clothes which cover both legs and armsin the evening
  • Parasites development in the human body can be controlled by taking modern prophylactic drugs regularly.
  • Applying mosquito repellant cream to the body.

Aedes species carry a virus which causes Dengue. It also carries germs which cause yellow fever.The Culex species carry filarial worms which cause elephantiasis. It is not a killing disease but causes discomfort due to large swelling of the legs and/ arm.

THE MOSQUITO