Wettable powders are made by:

Wettable powders are formulated by impregnating or coating an inert powder with an insecticide. This method allows the insecticide to be evenly distributed in a dry powder format, which can then be mixed with water for application. When water is added, the wettable powder suspends in the liquid, allowing for effective application on surfaces where pests are present.

This type of formulation is advantageous because it improves the stability and effectiveness of the insecticide during storage and application. The inert powder serves as a carrier that enhances the distribution of the active ingredient, ensuring that it adheres well to various surfaces when applied. This is particularly important in pest control, as it maximizes the contact opportunity between the insecticide and the target pest.

The other options describe different methods or formulations which do not align with the definition and characteristics of wettable powders. For instance, mixing insecticide with oil would describe an emulsifiable concentrate, while diluting insecticides in water typically pertains to liquid formulations, not powders. Lastly, using a high-pressure spray system relates to application techniques rather than the formulation process of wettable powders.