Dose-Response Tests on Red Flour Beetle and Confused Flour Beetle (Coleoptera: Tenebrionidae) Collected from Flour Mills in the United States

Adults of 14 field strains of the red flour beetle, Tribolium castaneum (Herbst), and 10 strains of confused flour beetle, Tribolium confusum Jacqueline DuVal, collected from flour mills were tested for resistance to malathion and dichlovos by topical application. Lethal dose estimates showed that all strains of T. castaneum were resistant to malathion and dichlorvos. Some strains showed the highest malathion resistance ever reported for this insect. Approximately half the strains of T. confusum tested were resistant to malathion and dichlorvos. T. castaneum was more resistant than T. confusum to both malathion and dichlorvos. There was a positive correlation of the lethal dose values for insecticide resistant strains of both species when compared with the survival of insects exposed to diagnostic doses. Therefore, survival of insects at a diagnostic dose maybe used to predict field efficacy of malathion and dichlorvos in these 2 pest species if resistance levels are low.