Effect of Temperature on Two Bio-Insecticides for the Control of Confused Flour Beetle (Coleoptera: Tenebrionidae)

Abstract

Stored product pests account for as much as 10% of food loss worldwide. Insects such as the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), are major pests of small grain in storage bins and grain elevators in Montana. Cold winters and dry summers have traditionally helped reduce levels of T. confusum in storage bins. However, with change in winter temperatures, this pest has become harder to manage using physical measures such as desiccation. The alternative, the chemical insecticide aluminum phosphide, is effective at controlling T. confusum in grain stores but is highly toxic to mammals, and recently there has been development of resistance in grain pests. Newly approved biologically based insecticides can provide appreciable levels of control without the drawbacks of aluminum phosphide. In this study, we tested the short-term effectiveness of spinosad (extracts of Saccharopolyspora spinosa Mertz and Yao; Actinomycetales: Pseudonocardiaceae) and Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) (a fungus-based insecticide) for their effectiveness against T. confusum under various temperature regimes. Insects exposed to low temperature (8 °C) sustained high rates of mortality (about 80% for the control and both treatments). When held at 16 °C, mortality was low for both biologically based insecticide treatments and the control. At 22 °C, spinosad induced high mortality, whereas at 25 °C, B. bassiana induced mortality. Overall, our results indicate that temperature affected the effectiveness of these biologically based insecticides against the confused flour beetle and may be important when considering implementation of control programs in grain stores.