## 4 Discussion
The concentrations tested here are generally comparable with those that have been used in similar studies testing inert materials in surfaces against insects [44; 45; 46; 47; 48]. We found that the formulation DE5 was usually less effective than the other two formulations for the majority of the combinations tested. However, even in the case of DE5, adult mortality reached 100% at a relatively short period of time, suggesting that the exposed individuals were largely affected even from the first days of their contact with the DE particles. [PERSON] and [PERSON] [28] reported that both DE5 and DE6 were effective for the control of major stored product beetle species as grain protectants, with DE6 to be slightly superior to DE5, which stands in agreement with the current observations. Nonetheless, all three formulations were able to kill all adults for all three species tested after 7 d of exposure, while, at least for _S. oryzae_ and _R. dominica_, adult mortality was 100% even after 3 d of exposure. [PERSON] [49] used 0.5 g/m2 of the commercial DE formulation Protect-It, and found that after 7 d, adults of _T. confusum_ were still alive and not heavily affected. Extremely low \"speed of kill\" after exposure to DEs is not desirable, as insects can escape from the treated area and colonize uninfested grain [1]. Nevertheless, in the case of _T. confusum_, larval mortality after exposure to inert dusts may be high [50], which can gradually eliminate the population through increased immature mortality. The current work sheds light on the application of DEs and zeolites on surfaces. It provides evidence that, in contrast with other insecticides, the type of surface may not be an important parameter here. Our study contributes further to the exploitation of the value of certain natural deposits of silicaceous materials as a means to control stored product insect pests. Considering the need to adopt non-chemical solutions in stored product protection, and taking into account that inert materials are compatible with sustainable and organic food production, additional work is needed to quantify the effectiveness of these formulations when applied in empty storage facilities under a variety of application scenarios. Conceptualization, C.G.A. ; Formal analysis, G.V.B. ; Funding acquisition, C.G.A. ; Investigation, G.V.B. ; Methodology, C.G.A. ; Supervision, C.G.A. ; Writing--original draft, G.V.B. ; Writing--review & editing, C.G.A. All authors have read and agreed to the published version of the manuscript. This research was partially funded by the project <<Integrated management of insect infestations in stored animal feed: Feed without pesticides>> (Project code: KMP6-0088130, acronym: SUSTAIN) under the framework of the Action <<Investment Plans of Innovation>> of the Operational Program <<Central Macedonia 2014-2020>>, and by the project <<Dialomite-Them>> (Project code: T2 EAK-03532) under the framework of the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH-CREATE-INNOVATE is co-funded by the European Regional Department Fund and Greece. Not applicable. **Acknowledgments:** We would like to thank [PERSON] (Olympus SA--Industrial Minerals, Assiros, Thessaloniki, Hellas) for providing the DE formulations for this study. **Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.