Laboratory experiments were carried out to assess the insecticidal effect of the diatomaceous earth formulation SilicoSec against larvae of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), in stored wheat (Triticum durum Desf.). Larvae were exposed to wheat treated with SilicoSec at 400 and 800 ppm and held at 20, 25, and 30°C and 55 and 75% RH. Larval mortality was assessed after 24 h, 48 h, 7 d, and 14 d of exposure in the treated wheat. At both dose rates, mortality increased with temperature, but this increase varied with the exposure interval. At short (≤48-h) exposures, larval mortality was significantly higher at 30°C than at the other two temperatures. In contrast, no significant differences were noted between 20 and 25°C. At longer exposures (≥7 d), the increase of temperature increased mortality at 800 ppm, but no significant differences were noted between 25 and 30°C at 400 ppm. Furthermore, significant differences in larval mortality were noted between the two humidity levels, but only at exposures ≥7 d. After 14 h of exposure, at both dose rates examined, the increase of temperature significantly decreased mortality. The results of the current study indicate that E. kuehniella is susceptible to SilicoSec, but temperature and relative humidity should be taken into consideration.