Zlatko Korunić

Diatomaceous earths, a group of natural insecticides

Abstract Diatomaceous earth (DE) is a geological deposit consisting of the fossilised skeletons of numerous species of siliceous marine and fresh water unicellular organisms, particularly diatoms and other algae. Many of these fossilised sedimentary layers originated at least 20 million years ago in the lakes and seas of the Eocene and Miocene epochs. After quarrying, crushing and milling, a fine light dust is obtained, containing porous particles with certain abrasive properties and the ability to absorb lipids to about three or more times the particle mass. Any diatomaceous earth with high oil absorbing capacity is a potential insecticide. Beyond the absorbing capacity, the size of particles, uniformity and shape of the particles, pH, and the purity of formulation affect the compounds insecticidal efficacy. Insecticidal diatomaceous earth should be a highly pure amorphous silica, having particles of equal diameter (

The effect of grain moisture content and temperature on the efficacy of diatomaceous earths from different geographical locations against stored-product beetles.

Abstract Source of diatomaceous earth (DE), insect species, grain moisture content, temperature, method of application and duration of exposure were all factors that influenced the mortality of stored-product insects. In all tests, regardless of the insect species, or source of DE, the lower the moisture content of grain, the greater the mortality. DEs from different geographical locations had different efficacies. The ranking of the different DEs remained similar at different moisture–temperature combinations. However, the mortality response with respect to moisture content did change among DEs from different sources for Sitophilus oryzae (L.), but not for Tribolium castaneum (Herbst). Of all the insects tested, Cryptolestes ferrugineus (Stephens) was the most sensitive to DE. Oryzaephilus surinamensis (L.) and S. oryzae were more tolerant than C. ferrugineus. Rhyzopertha dominica (F.) and T. castaneum were the most tolerant species tested. Applying DE as a dust was more effective than applying DE as an aqueous spray. For C. ferrugineus, lower temperatures reduced DE efficacy. The opposite was true for T. castaneum, as lower temperatures increased efficacy for most DEs tested. For S. oryzae some DEs had increased efficacy with lower temperatures and others had decreased efficacy with lower temperatures.

Rapid assessment of the insecticidal value of diatomaceous earths without conducting bioassays.

Abstract The efficacy of diatomaceous earth (DE) against insects depends greatly on several physical properties of the diatom particles. Ideally, active DE should have an high amorphous silicon dioxide content with a uniform particle size (less than 10 μm), a high oil sorption capacity, a large active surface, and very little clay and other impurities. The analysis of physical and chemical properties of DE is time-consuming and expensive, and can be conducted only by experts at specially equipped laboratories. Therefore, in the past, bioassay was considered the most important criterion for the assessment of the efficacy of DE against insects. These methods are relatively expensive and time-consuming also, since they require an expert and a well-equipped entomological laboratory. After conducting numerous experiments with 36 different diatomaceous earths or formulations collected from the U.S.A., Mexico, Canada, Australia, Japan, China, and Macedonia (Europe), results indicate that the efficacy of DE against insects depends on different properties of the diatom particles. Properties include the ability of DE particles to reduce bulk grain density (test weight), DE tapped and loose density, the tendency of DE particles to adhere on the grain surface, particle size distribution, diatom shape, and pH. It is possible to evaluate and to predict the insecticidal value of diatomaceous earth mainly by very simple and low-cost analysis of these properties of DE without bioassays or extensive physical and chemical analyses.

The effect of diatomaceous earth on grain quality

Abstract Protect-It is a newly developed diatomaceous earth (DE) based insecticide for stored-grain protection and structural treatment. It has proved effective at controlling stored-grain insects in laboratory tests at application rates well below other DE-based insecticides. This study examined the effect of Protect-It on quality, and physical and handling characteristics of cereals. Treatment of Hard Red Spring (HRS) wheat with either 50 or 300 ppm Protect-It had no significant effect on the milling, analytical, rheological or baking quality. The application of Protect-It on durum wheat did not affect the properties for high-quality pasta production at 50 ppm and 300 ppm, and treatment of barley at concentrations from 100 ppm to 900 ppm also showed no differences in malting quality characteristics. A different DE based insecticide, Insecto®, was used to examine the combined affect of DE and dockage on bulk density (test weight) on Hard Red Spring (HRS) wheat, durum wheat and barley. Both dockage and DE reduced bulk density. For HRS and durum wheat, the addition of 5%, 10%, or 15% dockage mitigated (less than 1 kg/hl) the reduction of bulk density when DE was applied. Protect-It treatment of HRS wheat, rye and barley gave 0.2% to 0.8% lower dielectric moisture values than before treatment, depending on the DE concentration and commodity. The effect was caused by physical effect of the dust on the grain, since wheat treated with DE had no actual loss of moisture. Protect-It did not affect the dielectric moisture content readings with oats and maize. In field tests, wheat treated with Protect-It at 75 ppm and 100 ppm, concentrations that controlled Cryptolestes ferrugineus (Stephens) and reduced Tribolium castaneum Herbst populations, did not cause a reduction in grain flow nor did it cause an increase in air-borne dust when grain was moved using a screw auger. Wheat treated with 300 ppm Protect-It had reduced grain-flow and caused an increase in air-borne dust. Bulk density of the wheat was measured before and after a spray (wet) application at 100 ppm or dust (dry) application at 75 and 100 ppm of Protect-It in both laboratory and field conditions. In the field, dry application of 75 ppm reduced bulk density by 1.6 to 2.5 kg/hl, 100 ppm by 2.0 to 2.8 kg/hl, and 300 ppm by 4.6 to 4.8 kg/hl. Protect-It reduced bulk density by 1.5 to 2.2 kg/hl at 100 ppm wet application.

Grain bulk density as affected by diatomaceous earth and application method

Abstract The effect of the enhanced diatomaceous earth (EDE) insecticide Protect-It ™ was studied at different concentrations on the bulk density of wheat, corn, barley, rye and oats at three moisture contents (12, 14 and 15% m.c., dry basis). The greatest changes in bulk density occurred when the concentration of EDE ranged from 50 to 200 parts per million (ppm). At concentrations greater than 500 ppm, bulk density decreased little with increased EDE concentrations. The bulk density reductions in all five grains tested were significantly higher for the grain at a dry basis moisture content of 15% than at 12%. The reduction in bulk density as a result of the EDE application was described mathematically using empirical equations. The bulk density of wheat was measured before and after the wet (suspension) or dry (dust) application at 100 and 300 ppm of EDE under laboratory conditions. The dry application caused a significantly greater reduction in wheat bulk density than did the wet application. Application of only 10 ppm of either marine or fresh-water DE significantly reduced the bulk density (about 1.3–1.8%, w/w, respectively) of 13.9% m.c. wheat without dockage. Twenty five various DE obtained from different regions of the world were tested for bulk density changes when applied to wheat at various concentrations. All DE decreased wheat bulk density, though there were significant differences between DE. The most active DE formulations against stored grain insects, such as Protect-It ™ , Dryacide ® , Insecto ® , Dicalite, DE Eu and DiaFil, also had the greatest effect on the bulk density.

Evaluation of natural diatomaceous earth deposits from south-eastern Europe for stored-grain protection: the effect of particle size.

BACKGROUND The use of diatomaceous earths (DEs) provides a promising alternative to the use of contact insecticides in stored-product IPM. Geographical origin and the physical properties of a given DE may affect its insecticidal activity. In the present study, DE samples were collected from different locations of south-eastern Europe, and their efficacy was evaluated in the laboratory against Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujiidae), Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). In addition, three fractions comprising particles of different size were obtained from each DE sample and assessed with regards to their effectiveness against the above stored-product insect pests. RESULTS DE from the Greek region of Elassona was the most effective against C. ferrugineus and S. oryzae, whereas the DE Kolubara 518, mined in the Serbian region of Kolubara, was the most effective against R. dominica. Smaller particles were more effective than larger particles against the three tested species, although significant differences in the efficacy of fractions containing particles of 0-150 microm and particles with sizes of < 45 microm were not always recorded. CONCLUSIONS Deposits from south-eastern Europe appeared to be very effective against the tested species, and therefore this region should be further evaluated as a source of development of commercial products. Particle size is a physical property that should always be taken into account during the DE manufacturing process, as it can strongly influence the insecticidal action of a given product.

Control of Insects in Post-Harvest: Inert Dusts and Mechanical Means

Residual chemicals are currently used to control stored-product insects pests that are found in granaries and food-processing facilities. Long-term use of these chemicals has resulted in the development of insect populations that are resistant to the common insecticides (e.g. malathion, chlorpyrifos-methyl, pirimiphos-methyl, fenitrothion or deltamethrin) (White and Leesch 1995). Inert dusts are used in a fashion similar to the residual chemicals, and hence offer a convenient alternative for the control of insect pests in grain-and food-processing industry installations such as flour mills, food warehouses and retail outlets.

Croatian diatomites and their possible application as a natural insecticide

In recent decades, there has been an increase in the use of diatomaceous earth (DE) as a natural insecticide because of its low mammalian toxicity, worker safety, low risk of food residues and the occurrence of resistant insect populations associated with the use of chemical insecticides.Therefore there is potential for research into known but previously undescribed Croatian mid-Miocene marine diatomites from the perspective of their potential as proper DE that could be mixed with plant extracts as a new formulation for grain storage protection. The marine diatomites belong to the Paratethyan near shore environment, deposited in the upwelling zone during a mid-Miocene temperate climate. Palaeontological, mineral and geochemical analyses were done on ten promising marly sediments from 26 outcrops and one borehole from the North Croatian Basin. The most important ingredient of diatomaceous sediments is silica (biogenic opal-Aand SiO2 bound in other silicate minerals including quartz, clay minerals, micas, etc.). The amorphous silica content of the tested Croatian diatomites is relatively low (<50%) in comparison with the Celatom® MN 51 standard (medium to high efficient DE) (73.6%), nevertheless they show insome part even slightly better efficacy against insects. It seems that the enhanced content of smectite in diatomaceous sediments also influences increased absorption of DE. Based on palaeontological results, the most efficient diatomites from the Podsusedsko Dolje and Markusevec (Medvednica Mt.) consist of the mid-sized planktonic Coscinodiscus group of species whereThalassionema nitzschioides dominate and is positively correlated with their absorption. The usage of Bostroms’ standard formula for getting opal-A from geochemical data was abandoned because of negative results and the modified Murdmaas’ formula for hemipelagic sediments was applied. Preliminary results on the aforementioned diatomite (as inert dusts) show good efficacy against tested insects Sitophilus oryzae (LINNAEUS), Tribolium castaneum (HERBST) and Rhyzopertha dominica (FABRICIUS).

Toxicity of naturally occurring compounds of Dalmatian (Croatia) Lamiaceae and Lauraceae to maize weevil ( Sitophilus zeamais motsch)

Maize weevil (Sitophilus zeamais Motsch.) is the major stored pest of Coleoptera order. It belongs to the group of economically important pests of stored grain. In Croatia, maize weevil can be more frequently found in storages of small-scale farms than in large storage facilities or silos. This is ascribed to its higher resistance to lower temperatures in distinction from the remaining pests of Sitophilus genus. Present measures of stored pest control are mainly based on application of synthetic insecticides and fumigants. However, their non-selective and uncritical application in storage facilities brings up some serious issues, such as toxic effects to the grain that is used in diet for people and livestock (Fishwick, 1988), and contamination of the environment (WMO, 1995). In practice in Croatia, phosphine is presently in use in stored pest control. However, fumigation with phosphine should be also limited for evident increase in the resistance of some pest species to a phosphine compound, which has been observed in more than 45 countries (Bell and Wilson, 1995). This means that phosphine in use can and has to be limited on the global level. Therefore, there is a necessity to find safe alternatives to the conventional insecticides and fumigants that would protect grain and its products (Rozman et al. 2006). This investigation proved that certain compounds (monoterpenes) of Dalmatian essential oil extracts of the families Lamiaceae and Lauraceae, respectively: lavender (Lavandula angustifolia Ch.), laurel (Laurus nobilis L.), rosemary (Rosmarinus officinalis L.) and thyme (Thymus vulgaris L.) exhibited toxic activity against maize weevil S. Zeamais which could be used as a new alternative in protection against the pest species.