A spray made from perlite, a type of volcanic glass, showed effective control of malaria-carrying mosquitoes, a study claims. In West Africa, researchers sprayed walls of a group of huts with "Imergard WP", another with a commonly-used insecticide, and the third with the combination of the two. Walls treated with Imergard initially killed the largest amount of 'Anopheles gambiae' mosquitoes.