## 1 Introduction  
In 1703, a man looking with his simple microscope a pond-weed's root observed many pretty structures to be attached in the roots. His descriptions and diagrams are the first certain records of a diatom--a unicellular aquatic plant related to the algae [1]. Fossils of such organisms, which contain high percentages (80-93%) of silicon dioxide (SiO\({}_{2}\)), an ingredient with insecticidal properties, formed along with other elements such as clay minerals, organic matter, quartz, calcium and magnesium carbonate [2]--the so-called diatomaceous earths (DE). Deposits of this fine white/gray material date back to the Eocene/Micene era and are scattered world-wide. For centuries, DE were used as insect repellents by human and animals. However, their mechanism of action was unknown, until [PERSON] and [PERSON] [3] attributed the insecticidal properties of DE as a result of dehydration and inability to replenish insect body water. Today, the mode of action of DE is generally accepted to have a desiccating effect on the insects, as diatoms have the ability to absorb the epicticular lipids of the insect cuticle [4]. This indicates that DE toxicity primarily depends on its physical properties and much less on its chemical composition [5]. DE is safe to use with an extremely low mammalian toxicity, does not react with other substances in the environment, does not affect grain end-use quality, provides long-term protection and is comparable in cost to other methodsof grain protection [6; 7; 8]. The pressing need to reduce the use of synthetic pesticides that cause the withdrawal of several active ingredients, the occurrence of resistant populations in several conventional insecticides [9; 10; 11] and consumer concerns over insecticide residues have led the grain industry in search for potential alternative substances such as DE [5; 12; 13; 14]. Drawbacks in DE use, such as their negative effect in the physical properties of grains and particularly in their bulk density [15; 16; 17] can be overshadowed with solutions such as combinations of DE with other reduced-risk methods [18; 19; 20; 21; 22]. There are several papers describing different factors that contribute in DE insecticide efficacy. Thanks to this extensive research, we now know that the insecticidal properties of DE mined around the world vary, depending on their geological and geographical origin [23; 24; 25; 26; 27]. Moreover, according to [PERSON] et al. [1], rocks that have been taken from different layers but the same locality, consist only of a selection of the species of the contributing communities that lived in variant conditions over millions of years. This, along with the fact that diatoms' morphological characteristics as well as their quota in the rock largely determine the insecticidal effectiveness of the DE powder, leads to the creation of different formulations around the world, many of which are currently commercially available for use at the postharvest stages of agricultural commodities [5; 7; 23; 28; 29]. Ideally, the DE should be a high purity amorphous silica of a uniformly small particle size that contains very little clay and less than 1% crystalline silica [7; 22; 30]. The DE rocks should be properly milled, the diatoms well-separated and, if possible, physically intact [7]. DE's adsorptive capacity for lipids, and its insecticidal efficacy, is also affected by the size, shape and surface topography of diatom species, uniformity of particles and the purity of the formulation [17; 28]; particles with a larger available active surface and of high purity with empty holes, being as dry as possible, have a higher sorption capacity for the lipids [5; 7; 28]. Furthermore, DE formulations with low tapped densities (<300 g/L), good adherence to the grain (>70%), a SiO\({}_{2}\) content greater than 80%, a pH below 8.5 and can reduce grain bulk density by more than 2.5 kg\(\cdot\)h\({}^{-1}\) when applied at a concentration of 50 ppm, are considered the most effective [31].