In recent years, awareness of the consequences of environmental pollution, the increasing cost of storage insecticides and the growing problem of insect resistance has led to pest management specialists reappraising inert dusts. Unlike conventional contact insecticides, inert dusts function through their physical properties and are, therefore, generally slower acting. Insect mortality is induced primarily as a result of desiccation: water loss is a consequence of the destruction of the cuticle. Silica aerogels adsorb the waxy particles from the cuticle surface and although diatomaceous
earths, having small dense particles of silicon dioxide, were said to abrade the cuticle, they also function by adsorption of wax. However, silica aerogels are more effective than diatomaceous earths or other inert dusts, retaining their activity even at elevated levels of relative humidity. Because the action of these materials is not dependent on metabolic pathways, it has been postulated that insects will not be selected genetically by the action of these dusts, so that physiological resistance will not occur. Nevertheless, it may be possible for insects to develop a behavioural response to the dust and avoid contact