Resistance to chemical treatments in insect pests of stored grain and its management.

Chemical insecticides, including fumigants, disinfestants and grain protectants, are essential components of grain insect pest management systems. This is particularly the case in warmer climates where insect infestation pressure is high. Because of health, safety, environmental and economic considerations, only a very limited number of chemicals is available for application to grain. A serious threat to the continued availability of these materials is the development of resistance in target pests. World-wide, the fumigant phosphine is by far the most important insect control treatment for stored grain. There are no practical alternatives to this unique material. However, resistance to this fumigant has developed in major pest species in many regions threatening its continued viability. Incidence of resistance to residual grain protectants is widespread. Populations of major pest species have developed resistance to organophosphates, pyrethroids, carbamates and other agents such as methoprene and Bacillus thuringiensis. In some regions, the situation is precarious with insect populations containing multiple resistances leaving no effective protectant options available. Because grain protection chemicals are a rare resource, the ability to manage or reduce the impact of resistance is a priority. Effective management relies on early detection which can only be achieved with a routine monitoring system and a research capability to estimate the impact of resistance. Development of effective strategies requires understanding of the grain storage system, the ecology of the pest insects, the response of insects to various chemicals and other treatments, and some insight into resistance genetics. We need to be able to answer the questions: How is resistance selected? and, What can we do to reduce selection? Implementation requires cooperation between scientists and storage managers across the system.