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There are three types of spraying used against mosquito vectors; residual spraying and space spraying - used against the adult mosquito - and larviciding - used against mosquito larvae.
Residual spraying involves mixing insecticide with solvent and spraying the internal surfaces of houses; it is an effective way of controlling mosquito numbers. It is important to understand the resting and breeding habits of the mosquito species in question to ensure appropriate areas are treated. Once the water has evaporated, the insecticide residue is active for months and kills mosquitoes when they land on treated surfaces. It can lower the incidence of malaria by reducing the life span of the female mosquito, reducing the mosquito population and reducing human–mosquito contact.
Residual spraying is relatively expensive and problems can arise if mosquitoes become resistant to the insecticide sprays, or walls are re-plastered after spraying.
Space spraying is often used as a control measure during malaria epidemics. A 'fog' of insecticide is sprayed into the air. It requires large resources of insecticide and specialist equipment to be effective, and has only a short-term effect. Pyrethroids are commonly used for space spraying.
Larviciding by chemical spraying of water sources is used to reduce mosquito breeding sites. However, environmentally friendly and non-toxic methods are preferred. Bacteria such as Bacillus thuringiensis can be sprayed into water. Mosquito larvae eat the bacteria and die because the bacteria act as a gut poison.
Guppy fish eat mosquito larvae and can be used as a form of biological control against mosquitoes in wells and irrigation channels.
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[WTD023989] Insecticide spraying.doc