Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera : Curculionidae) and Tribolium confusum du Val (Coleoptera : Tenebrionidae) on stored wheat: influence of dose rate, temperature and exposure interval

Laboratory experiments were conducted in order to assess the insecticidal effect of a diatomaceous earth formulation (Silicosec(R), Biofa GmbH, Germany) against Sitophilus oryzae and Tribolium confusum on stored wheat. Adults of the two species were exposed on wheat treated with diatomaceous earth at four dose rates: 0.25, 0.5, 1 and 1.5 g/kg of wheat, respectively. For each dose rate, the treated wheat was placed at 22degreesC, 25degreesC, 27degreesC, 30degreesC and 32degreesC. Dead adults were counted after 24 and 48 h, 7 and 14 d of exposure. After the 14-d interval, the live adults were removed and placed for 7 d in untreated wheat (in the case of S. oryzae) or untreated flour (in the case of T confusum), and the production of F-1 was recorded. For both species, dose rate, temperature and exposure interval significantly affected mortality (P<0.001). Mortality was higher at longer exposure intervals. The efficacy of SilicoSec against S. oryzae increased with temperature, but for T confusum mortality was lower at 32degreesC, compared to 30degreesC, for 24 and 48 h exposure intervals. Tribolium confusum proved less susceptible to SilicoSec than S. oryzae. In general, the rates of 1 and 1.5g/kg of wheat provided a satisfactory level of protection against the two species examined. For S. oryzae, F-1 emerged only at 22degreesC, in wheat treated with 0.25 or 0.5 g/kg. However, for T confusum, F-1 were recorded at 22degreesC for 0.5 g/kg and at 22degreesC, 25degreesC, 27degreesC and 30degreesC for 0.25 g/kg. (C) 2004 Elsevier Ltd. All rights reserved.