Current status and future perspectives for inert dusts for control of stored product insects

Inert dusts, particularly those based upon activated silicas, are finding increasing use as storage protectants in the grain industry. These materials can be classified into different groups depending on their composition and particle size. Non-silica dusts and those composed of coarse grain silicates, such as kaolin and sand, have been used traditionally as grain protectants by small-scale farmers in the developing world. More recently, materials including diatomaceous earths and silica aerogels, have been used increasingly in commercial storage in the developed world, replacing conventional chemicals. These materials have been shown to control a variety of common storage insect pests. They are most effective in conditions of low humidity because they induce mortality by causing desiccation; water is lost because the dusts remove the waxy layer of the cuticle of the exoskeleton by adsorption. These materials are most effective when applied as dusts but some retain activity even when applied as a water-based slurry. Modern dusts have overcome some of the health hazards resulting from inhalation, and concerns regarding abrasion of grain handling machinery are lessening. One modern dust, Dryacide, is used widely in Australia to treat the fabric of warehouse and grain handling machinery. However, this dust, Like all others, affects the flow characteristics of bulk grain and so cannot be used for treatment of grain in bulk storage and handling facilities. Synthetic dusts are effective in controlling primary pests of cereals and pulses, including Prostephanus truncatus, the Larger grain borer, a new and important pest on African farms. Thus, as well as being increasingly used in commercial farms, these materials may well replace conventional chemicals as protectants of stored grain in developing countries. The paper examines recent research related to the use of inert dusts and discusses their potential for use in large-scale, commercial storage and in small-scale applications in the developing world. (C) 1997 Elsevier Science Ltd.