Field trials with the diatomaceous earth SilicoSec® for treatment of empty rooms and bulk grain

Diatomaceous earths (DE) are fossil diatoms (phytoplankton) that contain silicon dioxide (SiO2), the particles absorb the waterproof lipids from the arthropod cuticle resulting in death through desiccation. The DE SilicoSec® is registered in Germany. The field trials presented here were performed in order to determine (1) the efficacy of SilicoSec® under temperate Central European climatic conditions, (2) the distribution in empty rooms and (3) the possible effect of different surface materials. For empty room treatment, a 41 m² storage room was treated with 20 g/m², the total surface treated including walls was 145 m². At 19 sampling points the amount of DE on the floor was determined. Distinctly less DE attached to the walls compared to the floor, and an uneven distribution on the floor ranging from 2.6 to 49.5 g/m² with a mean±SD of 15.4±14 g/m² per sampling point was measured. Additionally, test pieces with 5 different surface types were placed in the treatment room prior to the treatment. Adult Tribolium confusum and Cryptolestes ferrugineus were placed on all surfaces at 15 to 19°C and 65-81% r.h.. Mean corrected mortality after 14 d in T. confusum and C. ferrugineus was 94% and 65%, respectively. No significantly different mortality was recorded for T. confusum depending on surface type, but in C. ferrugineus significantly less beetles (20%) died on concrete flagstone compared to natural flagstone, glazed ceramic flagging, plywood and porcelain stoneware. For bulk grain, 10 t of wheat were treated with either 0.7 kg/t or 2 kg/t DE. Sitophilus granarius, Oryzaephilus surinamensis and C. ferrugineus adults were placed in vials with treated wheat together with data loggers and placed deep within the bulk for 19 d. Corrected mortality was around 90% for all treatments except for S. granarius at the lower dose where 60% mortality was achieved only.