A mechanical insecticide is made by mixing water with at least one type of silane to make a silane solution which is then mixed with diatomaceous earth until there is substantial deposition of the silane material on the diatomaceous earth material, to make a silanized diatomaceous earth. The silanized diatomaceous earth can be diluted with water and applied to vertical and overhead surfaces using a sprayer, for the control of insects. The silanized diatomaceous earth can also be dried into a powder for broadcast application, or mixed as a paste for brush/roller/caulk application.