Biological control of malaria

Malaria is a serious, sometimes fatal iliness caused by parasites spread by mosquitoes. Fortunately, there are simple, low-cost ways to control malaria without resorting to dangerous chemicals.

Note

Children and pregnant women are especially at risk from malaria.

Mosquitoes and malaria

In order to protect yourself from malaria, you must first understand the life cycle of mosquitoes. Female mosquitoes live 4-6 weeks. They take a blood meal on alternate days; they also consume liquids from wet surfaces. Male mosquitoes live 7-10 days. They feed on wet surfaces and fruit juices. They do not feed on blood.

Mosquitoes complete part of their life cycle in water. Mosquito eggs are laid in water; they pass through larval and pupal stages in water before they emerge as adult mosquitoes. The process takes about a week.

When a female mosquito feeds on a person infected with malaria parasites, the mosquito becomes infected. The parasites develop within a week inside the abdomen of the mosquito. When the mosquito next feeds, the parasites are released into the bloodstream of the healthy person.

Mosquito breeding habitats

Mosquitoes breed in: wells, ponds, ditches, pits, drains, water tanks, irrigation tanks, rainwater collectors, marshy areas, rice field irrigation channels, seepage spots, stagnant water in fields, stagnant rivers, fallow fields with ditches, in any small or large amount of still water.

Prevention of malaria

The most common method of malaria control involves the use of insecticides, mainly DDT. Insecticides destroy mosquitoes but also harm many other organisms-insects, aquatic animals, and people.

Larvae-eating fish

A number of fish species eat larvae, but not all can be used to control mosquitoes. Fish suitable for controlling mosquitoes must be:

- small so that they can reach the grassy pond edges which shelter mosquito larvae.

- prolific breeders to keep up with the fast-growing mosquito populations, and to compensate for losses to fish-eating birds.

- of no commercial value.

- able to live in turbid, polluted water and withstand temperature variation.

- surface feeders to control the floating mosquitoes.

- hardy enough to withstand transportation and handling.

- prefer to consume mosquito larvae.

Two fish which meet the above criteria

- Guppy (Poecilia reticulate)
- Gambusia (Gambusia affinis)

Each consumes 200-300 mosquito larvae per day.

Guppy

- Guppy live 3-5 years.

- They mature in 90 days, when males are 1.8 cm long and females 2.5 cm long.

- The female produces 50-200 offspring a month in broods of 57.

- The guppy breeding season in the tropics is from April to November.

- They are ideally suited to polluted waters, such as drains, ponds, pits, and sewage tanks.

- They cannot survive at low temperature (below 5 C) or in highly polluted water, such as water contaminated with industrial wastes.

Guppy

Gambusia

- Gambusia live 3-5 years.
- Males reach a maximum size of 4.5 cm and females 6.8 cm.
- Females mature in 3-6 months.
- Females produce 8-10 offspring per brood and usually produce 2-3 broods in a year.
- Gambusia are suited to fresh water, brackish water, and salt marshes.

Gambusia

Transporting fish

Fish can be transported short distances in any water filled tin or plastic container or plastic bag. For long distances, fish must be packed in water-filled polythene bags. The water must be oxygenated every 5-6 hours. (Slap the water surface with a small stick

Breeding larvae eating fish

Larvae-eating fish are available free from:
Fisheries Department, Delhi Administration, Timarpur, New Delhi or contact
Director, National Malaria Eradication Programme, 22-5 ham Nath Marg, New Delhi 1 1 0054.

Note

Fish are sensitive to chlorine.

Note

Mosquitoes travel about 3 km; so for best results, your control program should cover a 3-km radius around your village.

Fish multiplication in perennial village ponds

- Clear the pond of predatory fish by reseated netting or by application of mahua cake.

Release your breeding stock into a container of pond water to allow the fish to become acclimatized.

After 30 minutes, release the fish into the pond.

Usually there is enough fish food-zooplankton and phytoplankton-available in the pond and no artificial feed its needed

For faster growth of fish, dung and nitrogen fertilizers can be added to the pond.

Collect the multiplied fish in a tin container or elastic bucket.

Release in mosquito breeding sites

- Release the fish in mosquito breeding habitats at the rate of 510 males and females per square meter.

- Remove the grass from the edge of the pond or ditch where the fish will be released.

- Periodically net and remove predatory fish.

- Periodically check the fish for survival. Look for dead fish floating on the surface. Restock as needed. Try to discover what is killing the fish and remedy the problem. Consult the fisheries officer in your area for help.