Chemical strategies to control psocid pests in Australian stored grain

Abstract

In the past decade, psocids have emerged as important pests in grain storages in Australia. We evaluated the effectiveness of a range of chemical treatments including grain protectants, structural sprays and the fumigant phosphine and also investigated the possibility of resistance. We found that three species are of major importance: Liposcelis entomophila, L. bostrychophila and L. decolor and that they differ markedly in their tolerance to various chemicals. Liposcelis entomophila is tolerant to all protectants tested, whereas the other species are susceptible to organophosphates and synergised pyrethroids. Some strains of L. bostrychophila were detected with very strong resistance to phosphine, which could not be controlled with currently registered rates. These rates, however, could control the other two species. The key to controlling resistant L. bostrychophila is to apply low concentrations of phosphine for long periods (e.g., 15 days). Manipulating fumigation temperature can also reduce dose rates needed to control resistant strains. This information forms the basis of an integrated approach to managing psocid pests of stored grain in Australia.