Diatomaceous earth efficacy against Tribolium castaneum adults is influenced by dosage and exposure temperature

It is good practice for farmers to clean empty bins before storing newly harvested grain to prevent cross infestation. Unsanitary bins can harbor grain-infesting insects, including the red flour beetle, Tribolium castaneum (Herbst). The use of elevated temperatures has been proven to kill stored-product insects within 4-8 hours when temperatures of 50-60°C are reached and maintained in empty bins. Previous research has shown improved efficacy of diatomaceous earth (DE) dusts against stored-product insects at temperatures below 50°C. In this study, the efficacy of a DE formulation (Diafil) was examined against T. castaneum adults at 28^°C and 65% RH (control), 36, 42, 44 and 46^°C, and 19.3-30.1% RH. Laboratory trials were conducted to determine the efficacy of DE at 0, 2.5 and 5.0 g/m² on concrete arenas in Petri dishes to simulate the floor of empty bins. Twenty adults of T. castaneum were placed on untreated and DE treated concrete arenas for 4, 8, 12, and 24 h at the five temperatures. The efficacy of DE against T. castaneum adults increased with an increase in DE dosage and temperature. Adult survival was inversely related to exposure time at each temperature. At 28 and 36^oC, 4-24 h exposure to DE resulted in <100% mortality of adults. At 2.5 and 5.0 g/m² of DE and 46°C, 100% mortality of T. castaneum adults was observed at 12 h. The effectiveness at 46^oC was confounded by the increased mortality in the control treatment especially at 8-24 h DE exposures. All adults or nearly all adults were killed after 24 h at 42 and 44^oC at both DE dosages. The combination of diatomaceous earth and temperature can be used as an integrated approach for controlling insects in empty bins prior to storing newly harvested grain.