2015 Volume 30 Issue 1 Pages 7-12
The insecticidal efficacy of silica-gel powder against the German cockroach was remarkably affected by the particle size; the smaller size was more effective. The smallest size, as small as 470 mesh, produced good efficacy when applied at a rate of 3 g/m2 or more on the floor of a plastic arena against a susceptible strain and a field-collected colony that was highly resistant to organo-phosphoric insecticides. A particle size of 30 or 40 mesh sieves did not kill cockroaches. The 470 mesh silica-gel powder did not increase weight when exposed to room conditions of 26°C, 70％ RH for seven days, and the exposed 470 mesh silica-gel powder remained effective. When 470 mesh silica-gel powder was applied in a limited corner of the arena, the mortality was high in an inner circumference application but low in the center or in one side corner due to repellent behavior. Cockroaches exposed to 470 mesh silica-gel powder were dehydrated. The 470 mesh silica-gel powder did not show good efficacy against the larvae of the brown cockroach when applied at a rate of 10 g/m2. Other minerals passed through 200 mesh sieves, such as Kanuma pumice and Sakurajima volcanic ash, also killed German cockroaches when applied at the rate of 10 g/m2.
