What is indoor residual spraying (IRS) and when is it typically used?

• A. Deploying larvicides in standing water; not IRS.
• B. Spraying interior walls with residual insecticide to kill resting mosquitoes; used in malaria control, especially indoors in endemic areas.
• C. Use of insecticide-treated nets for personal protection (not IRS).
• D. Spraying outdoor vegetation with insecticide to reduce mosquito breeding in streams.

Answer: (B)

Indoor residual spraying means applying a long-lasting insecticide to the inside walls and other surfaces where mosquitoes tend to rest after feeding. The idea is that a mosquito that lands on treated walls picks up a lethal dose and dies, reducing both the mosquito population and the chance of malaria transmission. This approach works best in areas where the malaria vectors tend to rest indoors (endophilic mosquitoes) and where transmission is ongoing, so spraying homes indoors helps create a protective community effect.

This differs from spraying larval habitats, which targets mosquitoes in the water at the larval stage; insecticide-treated nets provide personal protection by keeping individuals guarded while sleeping but are not spraying interior walls; and outdoor spraying of vegetation targets outdoors and is aimed at adult mosquitoes or breeding sites rather than indoor resting surfaces.