## 1 Introduction  
Inert dusts, such as diatomaceous earths (DEs) and zeolites are promising alternatives to the use of traditional chemical methods in stored product protection [1]. A high number of studies have documented their efficacy against a wide range of insect species [2, 3, 4, 5, 6], while some studies have shown that these dusts are effective against fungi and bacteria that may co-infest the commodity along with insects [7]. In a recent review, [PERSON] et al. [8] illustrated the insecticidal potentials of DEs and related materials against a variety of insect taxa (Blattodea, Coleoptera, Diptera, Hemiptera, Hymenoptera and Lepidoptera), including household or agricultural pest species but also non-target insects. Similarly, [PERSON] et al. [9] reviewed the potentials of utilizing zeolites in food and agriculture including their important role in stored-pest management as inert dust applications. One of the incontestable advantages of inert materials and their use in stored product protection is the fact that, in most cases, they are of natural origin [10; 11]. The utilization of natural resource-based agents has been long regarded as an important parameter in modern pest control, and natural insecticides are now prioritized in terms of Integrated Pest Management (IPM) protocols [1]. At the same time, the exploitation of locally produced mineral materials can also be economically beneficial for the local economy of a given country [12; 13; 14]. [PERSON] et al. [12], in a thorough screening of DEs that were sampled from different countries of southeastern Europe, found certain deposits that had a high insecticidal efficacy, and could be further used in stored product protection. There are some studies indicating that this geographical area is rich in zeolites with good insecticidal value as well, with some of which to be evaluated successfully in stored product protection [15; 16; 17; 18]. [PERSON] [16] introduced a series of methods that can be used for the rapid evaluation of the insecticidal value of DEs, without the need to conduct bioassays, which could be adopted in the case of handling a large number of samples. This series of tests is mostly based on the particle size, but also to other parameters, such as pH and flowability [16]. [PERSON] et al. [19] reported that particle size is a crucial parameter and that the smaller the DE particles the higher the insecticidal efficacy against certain stored product beetle species. In a similar way, [PERSON] et al. [6] found that particle size of zeolites was important in terms of efficacy against insects, while particles with different sizes had a different degree of attachment in the insects' cuticle. Most of the above studies have been carried out with locally-produced deposits of amorphous silicacesous materials, such as DEs and zeolites, which have been proved equally effective, if not more effective, than silicates, which are artificially made [9; 11; 12; 13; 14; 19]. A plethora of data are available in the literature regarding the efficacy of inert materials for the control of major stored product insects. However, most of the published studies are focused on the utilization of inert materials as grain protectants, i.e., admixture with the bulked grains, despite the fact that there are numerous obstacles and disadvantages over this practice [15; 20; 21]. For instance, [PERSON] et al. [20] found that the commercially available DE formulation SilicoSec(r) (Biofa GmbH, Munsingen, Germany), was effective against the rice weevil, _Stiophilus oryzae_ (L.) (Coleoptera: Curculinotidae), but this efficacy varied according to the commodity on which the DE was applied. In the same context, [PERSON] et al. [21] reported that different formulations of zeolites could be effective for the control of _S. oryzae_ and the saw-toothed grain beetle, _Oryzaophilus surimensis_ (L.) (Coleoptera: Silvanidae) on grains, but their efficacy varied according to certain abiotic conditions, such as temperature and relative humidity.