9.1  Why are mosquito larval control strategies so important?

Remember the following key points about malaria transmission from previous study sessions:

• Malaria is transmitted by a mosquito vector.
• Not all mosquito types transmit malaria.
• The mosquito lays its eggs in water collections and the life cycle in water takes about 10 days to complete.

The implications of these facts are that:

• No mosquitoes means no malaria transmission.
• Making water collections unfavourable for mosquito breeding means few or no mosquitoes in the community.
• Killing the mosquito larvae in the water collections before they become adults and fly away, means fewer or no mosquitoes in the community.
• Achieving the above goals means very small or no malaria transmission.

Measures that rely on using insect-killing insecticides against the adult (flying) mosquitoes inside houses (spraying and using insecticide-treated bed nets (ITNs), as described in Study Sessions 10 and 11), mean that the mosquitoes must be susceptible to the chemicals if the controls are to be successful. Moreover, they kill only the mosquitoes that enter houses to bite people. However, you learned in Study Session 5 that some mosquitoes can bite people outside houses and transmit malaria. So we are starting the three sessions on malaria prevention with larval control for the following reasons:

1. Larval control is the first line of defense in malaria prevention and presents your first chance of breaking the malaria transmission cycle.
2. The mosquito larvae are not flying insects; it is easy to find the water collections where they are developing to become the adult mosquitoes that will start biting people and transmitting malaria.
3. If people in your village get sick and die of malaria, you have to implement more expensive and complicated mosquito prevention and curative measures to protect the community.
4. Many of the larval control measures are inexpensive; they can be implemented by educating, mobilising and coordinating community members to clean their environment.
5. Compared to other measures, the chemical methods of larval control are also not very expensive and are simple enough to be applied by you or volunteer community health workers.