Activity of amorphous diatomaceous earths on stored-product pests - Study of abrasive and sorptive effects

The present study examined the morphological and physiological effects of a morphous diatomaceous earth against the stored product pests S. granarius, T. molitor and T. confusum. Diatomaceous earth, namely Fossil Shield(R) and Dryacide(R) increased the mortality rare of this insects. After contact wi th Fossil Shield(R) the individuals of S. granarius had significant lost of weight and reduced their water content respectively. This showed that sili ca dusts break the water barrier of the cuticle. However, it increases the transpiration rare of water across the cuticle and the insect died past sev eral rimes through dehydration. As well, an addition of food affected the e ffectiveness of dusts against insects. A lot of stored product beetles will be able to produce metabolic water of feed substrates. This ability protec ts and weaves contrary to the loss of water. Diatomaceous earth's can be ef fective primarily through the sorptive properties of the hygroscopic partic les. One day after dust treatment a significant weight loss of T. molitor p upae was recorded. The exposure to the silica dust Fossil Shield(R) caused partly an incomplete metamorphosis and death of the individuals. Pupae dipp ed in Fossil Shield" or abrasive aluminium dust and rolled for further five minutes, reduced not significant: higher their weight as unrolled exuvial stages. The morphological analyses of treated insects under the Scanning El ectron Microscope showed, that the dust covered the hole integument. Partly the silica particles sunk into the cuticle. After application of Fossil Sh ield" at the cuticle of adults, T: molitor, did not: show any wax layer. Al so it could not be found once blocked by stigma of the mealworm. The dust p articles accumulated around the respiration openings and they partly overgr ew.