Laboratory experiments were conducted to determine the effect of Silicosec by using contact and oral bioassay methods on survival of 1–7 days old adults of Oryzaeohilus surinamensis (L.) and Tribolium castaneum (Herbst) at 27±2°C and 65±5% RH. For contact method adult of these species were exposed to five doses of Silicosec for 3 days on plastic Petri dishes while in the case of oral bioassay technique the species were exposed to maize treated with five doses of Silicosec in small glass vials for 10 days. After exposure the initial mortality was recorded. For O. surinamensis in oral and contact methods 99% mortality was achieved at 8 333 ppm after 10 days and 165 ppm after 3 days, respectively, for T. castaneum 75% mortality achieved at 25 000 ppm after 10 days and 165 ppm after 3 days in the same order. For the oral method LC50 values for O. surinamensis and T. castaneum were 50 and 133 ppm, respectively after 10 days, while for the contact method these criteria were 8 and 57 ppm, respectively after 3 days. The results revealed that Silicosec with contact method could have more deleterious effect compared to the other method, and O. surinamensis was more susceptible to Silicosec than T. castaneum in either bioassay methods