Initial and delayed mortality of Rhyzopertha dominica (Col.: Bostrichidae) and Tribolium castaneum (Col.: Tenebrionidae) adults exposed to Silico-Sec® formulation of diatomaceous earth

Efficacy of temperature and exposure interval on the toxicity of Silico-Sec®, a diatomaceous earth formulation, was determined on 7-14 days old adults of Rhyzopertha dominica (F.) and Tribolium castaneum Herbst under laboratory conditions at 22, 27, 32 ºC and 65 ± 5% R.H. Insects were exposed for 8-72 hours to diatomaceous earth at the rate of 10 g/m2 on a filter paper inside plastic Petri dishes separately. Then the initial mortality was counted and, to determine delayed mortality, live individuals were held for a week in clean Petri dishes without food at the same conditions of previous experiment. LT50 values of initial mortality for R. dominica were 21, 12 and 9 hours at 22, 27, 32 ºC, respectively, and in the case of T. castaneum, they were 52, 27 and 18 hours at the same temperatures. The LT50 values indicated that R. dominica was more sensitive to Silico-Sec® than T. castaneum under identical conditions. Results indicated that the initial mortality of both species was significantly lower at 22 ºC in comparison with 27 and 32 ºC, and a direct relationship between temperature and exposure period was observed. Mortality percentage of both storage pests was higher after a week than initial mortality. Therefore, Silico-Sec® can be recommended as a structural treatment of stored grain facilities.