Comparison of three different wood ashes and diatomaceous earth in controlling the maize weevil under laboratory conditions

We studied the insecticidal effects of ashes from three different tree species (common beech, Norway spruce, and black locust) on the mortality of Sitophilus zeamais adults under laboratory conditions. A diatomaceous earth formulation, SilicoSec® was used as a positive control. We studied the contact effects of ashes on adults and the insecticidal effect of ash mixed with wheat grain. The experiment was carried out at three different temperatures (15, 20 and 25 °C) and at two different relative humidity [r.h.] values (55% and 75%). The study on contact effects (immediate mortality and delayed mortality) was carried out in Petri dishes, where we applied ash in two concentrations, 10 and 20 g/m2. After 7 d there was more than 97% mortality for the beetles in all three wood ashes at 25 °C and 55% R.h., while after 14 d wood ash of Norway spruce showed the highest effectiveness (87%) at 20 °C and 55% R.h. 96% mortality was recorded at 20 °C and 55%, when SilicoSec® was applied. The experiment with the mixture of ashes and grains was performed by mixing 2.5 or 5 w% of ash with wheat. In both approaches, we established that lower R.h. in combination with higher temperatures led to higher adult mortality rates. Regardless of the approach, the preparation concentrations did not influence adult mortality. The most efficient ash was that of Norway spruce, yet we attribute its effectiveness not only to its highest content of SiO2 (11.68%) but also to the other ingredients in ash, which can enhance its hygroscopic properties. Our research demonstrated that wood ash can efficiently protect stored crops from maize weevils. However, before introducing wood ash into the systems of protecting stored wheat grains against harmful insects, the influence of concentrations of ashes and their hygroscopic properties should be studied.