Beetles of the genus Sitophilus are among the most important pests of stored grain worldwide, as confirmed by the fact that three species of this genus are among the 10 most studied pests of stored products. In our research, we tested the contact action of powders on S. oryzae beetles, the repellent effect on S. zeamais beetles, and for S. granarius beetles, we used plant aqueous extracts. Due to the increasing awareness of the dangers of synthetic insecticides to the environment, plant biopesticides, due to their environmentally friendly nature, have a promising future, as they can act as insecticides or repellents for insects. For this reason, we decided to prepare biodegradable plant powders and aqueous extracts from the following plant species: Solidago canadensis, Solidago gigantea, Rhus typhina, Amorpha fruticosa and Ailanthus altissima. These are invasive alien species, whose presence threatens native indigenous species in the ecosystem and requires their removal from the environment. Since they are scheduled for incineration, we decided to investigate whether they can be useful for controlling pests from the Situphilus genus. In order to assess the effectiveness of plant powders, we also used inert powders: quartz, zeolite, SilicoSec® and spruce wood ash. In both studies, where we had contact action, it turned out that inert powders are more insecticidally effective, as SilicoSec® was the most effective in controlling S. oryzae, where 100% mortality was observed already 8 days after treatment at 20 and 25 °C for 55 % RH, and at 20 °C and 75 % RH after 14 days. In the study using S. zeamais, we confirmed the results of our first study that dusts of non-native invasive species are insecticidally ineffective, and again SilicoSec® was the most effective, as the survival rate fell below 15 % after 14 days of treatment. In all three experiments, temperature played an important insecticidal role. The results showed that the highest mortality was observed at 10 °C, while the lowest was at 25 °C. We confirmed that S. granarius is more cold-resistant than S. oryzae or S. zeamais and consequently better control is expected at lower temperatures. Aqueous extracts proved ineffective, as a greater effect was detected only immediately after 24 hours, followed by a drop in effectiveness, as aqueous extracts dry out during this period and thus lose their volatile properties. In the progeny test, plant powders of invasive plant species showed a reduction in the number of S. granarius progeny by approximately 30 % compared to the control, which is not negligible, but this is still not even close to the effectiveness shown by SilicoSec®, zeolite and wood ash, where there were practically no progeny at all.
|
