Efficacy of inert materials, plant powders and their mixtures against Sitophilus oryzae in maize: searching for improved combinations

The rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), is an important pest of stored cereals worldwide. This study evaluated the efficacy of inert materials, plant powders and their mixtures against S. oryzae in maize grain at different temperatures (15, 20, 25 and 30 °C) and relative humidities (RH; 55 and 75%). Adult mortality was assessed after 7, 14 and 21 days of exposure. After the 21-day parental exposure period, surviving adults were removed and F1 emergence was assessed after 56 days under standardized conditions. Treatment type, temperature, RH and exposure period significantly affected adult mortality and progeny production. Among the tested materials, SilicoSec® showed the most consistent efficacy. At 900 ppm, corrected mortality exceeded 90% under most environmental conditions after 21 days and reached 99.23%. SilicoSec® at 900 ppm also provided the most consistent suppression of F1 emergence under conditions favorable for population development. In contrast, the locally sourced diatomaceous earth, quartz sand, zeolite, Norway spruce wood ash, giant goldenrod and Canadian goldenrod showed lower or more variable efficacy. The reduced-component mixtures did not consistently improve adult mortality or F1 suppression. F1 emergence was strongly influenced by parental exposure conditions, with very low emergence following exposure at 15 °C, generally increasing toward 25 °C and declining again at 30 °C in many treatments. Overall, SilicoSec® was the most reliable treatment under the tested laboratory conditions, whereas the alternative materials and mixtures require further optimization before their practical potential can be established.