Insecticide resistance in the major coleopterous pests of stored grain in southern Queensland

Abstract

The extent and level of resistance to insecticides in the tenebrionid Tribolium castaneum, the curculionid Sitophilus oryzae and the bostrichid Rhyzopertha dominica was assessed using individuals collected from central storages, grain merchants and farms in Queensland in 1983-84. The beetles were initilly screened with a discriminating dose of insecticide; T. castaneum and S. oryzae with fenitrothion at 0.08 and 0.02 g/litre, respectively, and R. dominica with carbaryl at 0.02 g/litre or bioresmethrin at 0.02 g/litre. If this indicated the presence of resistance, the insects were subjected to a full dose-mortality bioassay to determine the level of resistance. Low level resistance to fenitrothion was found in a few strains of T. castaneum ( x 2-3) and in many strains of S. oryzae ( x 2-4). Low level resistance was found to carbaryl in R. dominica ( x 2-4), but there was no resistance to bioresmethrin. Resistance to fenitrothion in T. castaneum and S. oryzae was not economically significant, but as some resistant individuals of R. dominica will survive in carbaryl-treated grain, resistance to this chemical will result in an increased proportion of control failures. Resistant and susceptible reference strains of these 3 coleopterans reared in the laboratory for several years, were found to be similar to resistant and susceptible field populations in their response to these insecticides.