Factors affecting the insecticidal efficacy of the diatomaceous earth formulation SilicoSec® against adults of the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

The insecticidal efficacy of the diatomaceous earth formulation SilicoSec (R) (Biofa GmbH) against adults of the rice weevil, Sitophilus oryzae, was evaluated in laboratory experiments on stored wheat. Bioassays were conducted at three temperature levels, 22, 27 and 30 degrees C, two relative humidity (rh) levels, 55 and 65%, and four dose rates, 0.25, 0.5, 1 and 1.5 g of SilicoSeco (R)/kg of wheat. Three different aged-adult groups, 1, 2 and 7 d-old, were exposed. The mortality of exposed adults increased with the exposure interval and dose rate. Also, the increase of temperature increased S. oryzae mortality in all exposure intervals examined. The increase of rh from 55 to 65% caused a significant decrease in S. oryzae mortality. The age of the exposed individuals did not have a direct effect on SilicoSeco efficacy.