Development of Grain Protectants for Use in Australia

ABSTRACT Since the early 1960's Austalia's high standard of pest control in stored grain has depended chiefly on the application of grain protectants. Malathion was used until 1976–79, malathion-resistant strains then became predominant so alternative insecticides, chiefly fenitrothion but also pirimiphos-methyl and chlorpyrifos-methyl, were substituted progressively in the various States. Addition of synergised bioresmethrin was required in areas, initally the Eastern States, where prevalent strains of Rhyzopertha dominica were cross-resistant to the newer materials. Development of appropriate protectant treatments commences with surveys of insecticide-resistant strains in storages and establishment of laboratory cultures of significant strains. Initial screening of candidate compounds is done in the laboratory using impregnated-paper assays and treated-grain assays. Field testing is then carried out in commercial storages with periodic grain samples tested in laboratory bioassays and chemical assays. Compounds under development which have potential to control all species include methacrifos, deltamethrin, cyfluthrin and cypermethrin. Fenvalerate, permethrin and phenothrin have potential to control Rhyzopertha dominica . Data generated include residue levels both on grain and in major grain products e.g. bran, germ, flour and bread. Data are also generated on the rate of breakdown of these compounds at a range of grain temperatures and grain moistures. All residue levels must conform to maximum residue limits recommended by the Codex Alimentarius Commission.