Basic 8 · Science · Life Cycle of the Anopheles Mosquito
The Anopheles Mosquito
In this topic you will describe the life cycle and economic importance of the Anopheles mosquito, and discuss its impact on human beings and how it can be controlled.
By the end of these notes you should be able to:
- Describe the life cycle of the Anopheles mosquito
- Explain how the mosquito spreads malaria and affects the economy
- Discuss ways of controlling the mosquito
What you already know
- Life cycles of insects
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Cycles
- Sub-strand
- Life Cycle of the Anopheles Mosquito
- Indicator
- B8.2.2.1.1 – Describe the life cycle and economic importance of the Anopheles mosquito
Introduction
One of the most dangerous animals in the world is smaller than your fingernail. The female Anopheles mosquito is responsible for spreading malaria.
1. Features of the Mosquito
Anopheles is an insect with a head, a thorax, an abdomen, six legs, two wings and a long, needle-like mouthpart called a proboscis. It can be recognised by the way it rests: its body stands at an angle of about 45° to the surface, with its head down and its abdomen raised. The more common Culex mosquito rests with its body nearly parallel to the surface. Only the female Anopheles sucks blood, which she needs in order to produce eggs. The male feeds on nectar and plant juices.
2. The Four Stages
| Stage | Where | Features | Duration (approx.) |
|---|---|---|---|
| egg | on the surface of still water | laid singly, with floats | 2–3 days |
| larva | in water | lies parallel to the surface, breathes air through spiracles | about 7 days |
| pupa | in water | comma-shaped, does not feed | 2–3 days |
| adult | in the air | flies, mates and feeds | up to a few weeks |
This is complete metamorphosis, meaning the young look entirely unlike the adult. In warm places, the cycle from egg to adult takes about 10 to 14 days, so a puddle can produce a new generation of mosquitoes in two weeks.
3. Breeding Places
Mosquitoes breed in still water. Blocked gutters, old tyres, empty cans, broken pots and flower vases all hold water. After the rains, these places fill up, and mosquito numbers rise. Anopheles often prefers clean, sunlit pools, such as puddles and irrigated fields. Learners should look around their homes and schools for water that does not flow.
4. Comparing Mosquitoes
| Feature | Anopheles | Culex |
|---|---|---|
| resting angle | about 45° | nearly parallel |
| eggs | laid singly | laid in rafts |
| larvae | lie parallel to the surface | hang at an angle |
| disease | malaria | filariasis, among others |
New words
- proboscis
- The long mouthpart of a mosquito.
- larva
- The feeding young stage of an insect.
- pupa
- The resting stage before an adult.
- metamorphosis
- A complete change of form during life.
Summary
- The female Anopheles bites and rests at an angle.
- The life cycle has four stages: egg, larva, pupa and adult.
- Mosquitoes breed in still water.
Class activity: Life Cycle Model
- Draw the four stages in a circle with arrows.
- Note where each stage lives.
- Discuss which stage is the easiest to control.
You need: Sealed mosquito specimen, Printed mosquito life-cycle diagram, Mosquito net
Exercises
Answer in your exercise book first, then check your answers.
1. Which mosquito bites humans for blood?
- A. the female
- B. the male
- C. the larva
- D. the pupa
Show answer
Answer: the femaleBlood for eggs.2. The correct order of the life cycle is…
- A. egg, larva, pupa, adult
- B. egg, pupa, larva, adult
- C. larva, egg, pupa, adult
- D. pupa, larva, egg, adult
Show answer
Answer: egg, larva, pupa, adultStages.3. Mosquitoes breed in still water.
- A. True
- B. False
Show answer
Answer: TrueBreeding.4. The long mouthpart of a mosquito is the ______.
Show answer
Answer: proboscisMouthpart.5. How can you recognise a resting Anopheles mosquito?
Show answer
Answer: Its body is held at about 45° to the surface with the abdomen raised.Posture.6. Why do mosquito numbers rise after the rains?
Show answer
Answer: Rain fills containers and pools with still water, where mosquitoes breed.Breeding sites.
Lesson 2
- Strand
- Cycles
- Sub-strand
- Life Cycle of the Anopheles Mosquito
- Indicator
- B8.2.2.1.1 – Describe the life cycle and economic importance of the Anopheles mosquito
Introduction
A tiny bite can cost a family many days of work and school. The harm caused by Anopheles goes far beyond a fever.
1. How Malaria Spreads
- A female Anopheles bites a person who has malaria.
- She takes in the Plasmodium parasite with the blood.
- The parasite develops inside the mosquito.
- She bites a healthy person and injects the parasite with her saliva.
- The parasites travel to the liver and multiply.
- They enter red blood cells and destroy them.
Plasmodium is a single-celled parasite, not a virus. The mosquito is a vector, which means it carries a disease from one host to another without being the cause of it.
2. Symptoms of Malaria
Signs usually appear about 10 to 15 days after the bite. They include fever, chills, headache, vomiting and body aches. Severe malaria can cause anaemia, confusion and death, especially in children under five and in pregnant women. Anyone with these symptoms should get tested at a health facility, not simply buy medicine. Treatment with the correct drugs must be completed even if the person feels better.
3. Economic Importance
| Area | Effect |
|---|---|
| health | money spent on tests, drugs and hospital care |
| work | lost days of work and lower income |
| school | absence and poorer learning |
| farming | lower harvests when farmers fall ill |
| government | large spending on control programmes |
| tourism | some visitors stay away from malaria areas |
These costs fall hardest on the poor. Economists speak of malaria as both a cause and a result of poverty, since poor households struggle to afford protection, and illness makes them poorer still.
4. Do Mosquitoes Have Any Value?
Mosquito larvae provide food for fish and other water animals, and adult mosquitoes feed some birds, bats and dragonflies. Male mosquitoes also feed on nectar and help to pollinate some plants. Scientists study the balance between controlling mosquitoes and keeping nature healthy. Still, the harm done by Anopheles to people is far greater than these small benefits.
New words
- Plasmodium
- The parasite that causes malaria.
- vector
- An organism that carries disease.
- parasite
- An organism living on or in another, causing harm.
- anaemia
- A shortage of red blood cells.
Summary
- Malaria is caused by Plasmodium, spread by female Anopheles.
- Malaria causes fever and can be fatal.
- Malaria reduces income, learning and national productivity.
Class activity: Cost of Malaria
- List the costs to a family when one member gets malaria.
- Estimate days of work and school lost.
- Share your findings.
You need: Sealed mosquito specimen, Printed mosquito life-cycle diagram, Mosquito net
Exercises
Answer in your exercise book first, then check your answers.
1. Malaria is caused by…
- A. Plasmodium
- B. a virus
- C. a worm
- D. dirty water
Show answer
Answer: PlasmodiumParasite.2. The mosquito is called a vector because it…
- A. carries disease
- B. causes hunger
- C. eats crops
- D. lays eggs
Show answer
Answer: carries diseaseTransmission.3. Malaria can cause death.
- A. True
- B. False
Show answer
Answer: TrueSevere malaria.4. A shortage of red blood cells is ______.
Show answer
Answer: anaemiaBlood.5. State three symptoms of malaria.
Show answer
Answer: Fever, chills and headache.Any three.6. Explain how malaria affects the economy.
Show answer
Answer: Sick workers lose income, families and government pay for care, and absent learners learn less.Economy.
Lesson 3
- Strand
- Cycles
- Sub-strand
- Life Cycle of the Anopheles Mosquito
- Indicator
- B8.2.2.1.2 – Discuss the impact of the Anopheles mosquito on humans and how it can be controlled
Introduction
Malaria is both preventable and treatable. Controlling it requires action at home, in communities and by the government.
1. Controlling Breeding
| Stage | Control |
|---|---|
| eggs and larvae | drain stagnant water, clear gutters and fill puddles |
| larvae | oil on water, larvicides, fish that eat larvae |
| pupae | drain water |
| adults | treated nets, indoor spraying and repellents |
Attacking the mosquito before it can fly is often the most effective approach, since many larvae gather in one place. Ghana has used biological larvicide in some towns and carries out indoor residual spraying in selected districts.
2. Protecting People
- Sleep under an insecticide-treated net every night.
- Screen doors and windows.
- Wear long clothes in the evening.
- Use repellents and approved coils carefully.
- Keep the surroundings clean.
- Seek early testing and treatment.
3. Medicines and Vaccines
Artemisinin-based combination therapy (ACT) is the recommended treatment for uncomplicated malaria in Ghana. Pregnant women receive preventive medicine during antenatal care. In 2019, Ghana was among the first countries to start giving children the RTS,S malaria vaccine in a pilot programme. Scientists are still improving vaccines. Yet vaccines work best together with nets and other measures.
4. Challenges
Mosquitoes can become resistant to insecticides, and parasites can become resistant to drugs. Overusing or misusing them speeds this up. For this reason, you should not take antimalarial medicine without a test, or stop when you feel better. Some people also fail to use nets, or use them for fishing or fencing. Education is therefore a key part of malaria control.
Safety: Do not spray insecticide directly on food, skin or near infants. Follow the label instructions and store chemicals out of children's reach.
New words
- insecticide
- A chemical that kills insects.
- larvicide
- A chemical that kills larvae.
- resistance
- Surviving a drug or chemical that once worked.
- vaccine
- A substance that trains the body to fight disease.
Summary
- Removing stagnant water prevents mosquitoes from breeding.
- Treated nets, spraying and early treatment protect people.
- Resistance means that drugs and insecticides must be used correctly.
Class activity: Mosquito Patrol
- Inspect your school compound for still water.
- Remove or report each site.
- Write a short report.
You need: Sealed mosquito specimen, Printed mosquito life-cycle diagram, Mosquito net
Exercises
Answer in your exercise book first, then check your answers.
1. The best protection at night is…
- A. an insecticide-treated net
- B. a fan
- C. open windows
- D. a bright light
Show answer
Answer: an insecticide-treated netBarrier.2. Removing still water stops…
- A. breeding
- B. flying
- C. biting only
- D. sleeping
Show answer
Answer: breedingLife cycle.3. Mosquitoes can become resistant to insecticides.
- A. True
- B. False
Show answer
Answer: TrueResistance.4. A chemical that kills larvae is a ______.
Show answer
Answer: larvicideLarvae.5. State three ways of controlling mosquitoes.
Show answer
Answer: Draining stagnant water, spraying and using treated nets.Any three.6. Why should malaria drugs be taken only after a test and completed?
Show answer
Answer: To treat the correct illness and to prevent drug resistance.Medicine.
Homework
- Write a malaria prevention message for your community.