## 4 Discussion  
Our study focused on analysis of the efficacy of plant powders from invasive alien plant species against rice weeevil. Plant powders were applied alone or enhanced with two other inert dusts, diatomaceous earth and wood ash. Our study found that the mortality of individuals was significantly influenced by relative humidity and temperature. The same held true for treatments in which we used milled leaves of alien invasive plants, as well as for treatments in which we studied the synergistic effects of milled leaves with the two types of inert dust at a reduced dose. The fact that increased temperature and decreased relative humidity improved the effects (higher mortality of beetles) of inert dusts (wood ash, diatomaceous earth, zeolites... ) was confirmed by [4; 15; 16]. It is known, for inert dusts, that they have the highest efficacy at low humidity [17] because they cause desiccation. Insects can lose water because the dusts remove the waxy layer of the cuticle by adsorption. Low R.h. was the main factor in treatments, where we have added wood ash and diatomaceous earth. To date, studies of the effects of milled plant material in independent applications have also reported low mortality of beetles [5], as established in the first part of our research. Due to the already known negative influence of inert dust on stored grains [17], reducing the quantity of inert dust is essential. Synergistic effects of inert dusts combined with plant insecticides have already been confirmed by some studies, and the effects are primarily connected with the use of essential oils [1], as well as the use of plant powders. Combinations of essential oils and diatomaceous earth are supposed to cause additional stress to storage insect pests, as essential oils increase the movement of pests and consequently facilitate the effects of diatomaceous earth. It is confirmed [18] that adding diatomaceous earth to powders from _Piper guinenes_ and _Senna siamea_ improved the effects of the powders and thus achieved higher mortality than from their independent application. At lower humidity and higher temperature, our study achieved a comparable mortality (over 90%) during treatments in which a lower concentration of ash was added to powders (bioassay 2), and in the treatment in which we used wood ash at a higher concentration. Comparable insectical effects during the single application of wood ash and the application of combinations of wood ash and four powders from IAPs were also achieved at the lower temperature and lower humidity, yet the mortality after the 21 st day of exposure did not exceed 95%. At the higher relative humidity, we achieved mortality in individual treatments that was higher than 40% (control treatment-wood ash) and 90% (a combination of wood ash and Canada goldenrod) only after 21 days. Adding diatomaceous earth to the milled leaves of IAPs improved the insectical properties of the plant powders, though not as significantly as when wood ash was added. The combined use of plant insecticides (milled plant parts) and wood ash was recommended in the study by [19], and this application is supposed to be primarily useful for farms in less developed parts of the world, where this treatment would considerably lower the costs of pest suppression. To date, studies on the efficacy of wood ash for the suppression of storage pests have not confirmed their negative effects on stored wheat [3], and the mortality of beetles has also not been shown to be affected by the concentration of wood ash [4]. On the other hand, an increasing number of studies have proven that it makes sense to reduce the quantity of diatomaceous earth in treatments [1; 17] because of its demonstrated negative effects, such as its adverse effects on the physical and mechanical properties of grain. For this reason, our study involved further decreases in the doses of the selected inert dusts, i.e., diatomaceous earth and spruce wood ash (relative to previous doses).