Efficacy of diatomaceous earth dust under modified atmospheres against some stored grain insects

Studies were conducted to determine the efficacy of Diatomaceous earth (DE) alone and under three modified atmospheres (MAs) of carbon dioxide (C02) and high Nitrogen (N2) content on four insect species infesting stored grains in Egypt. DE was tested at 0.3% and 0.6% w/w alone and under MAs of 30, 60 and 80% CO2 and 99% N2 against adults of Sitophilus oryzae (L. ). Rhizopertha dominica (F.), Tribolium castaneum (Herbst.) and Trogoderma granarium (Everts) larvae_ Investigations were conducted inside gas-tight steel bins (each of 0.5 m. ), which were situated at premises of Faculty of Agriculture, Moshtohor, Zagazig University Obtained results revealed that, the effectiveness depends on the dust concentration. exposure period and tested insect species and the type of the tested MA. T. granarium larvae were found more tolerant to DE compared to other tested insect sp ecies. In respect to MAs of 30, 60 and 80% C02 and 99% N2 alone, the efficacy was depending on gas concentration, exposure period and insect species. which the effectiveness increased with increasing gas concentration and exposure period. T. granarium larvae (active and diapaused) were found more tolerant than the adults of the other tested insects. The combined action of DE with the four MAs figures used depends mainly on dust concentration, exposure time, insect species and type of MA. The results of the combined effect of the DE dust under MAs to the tested insects, showed improved mortality values than those achieved with each component separately at all the exposure periods. With DE at 0.3 and 0. 6% under MAs of 30% and 60% of C02 the resultant effect was synergistic or additive with adults of the tested insects while, with MA of 80% C02 the effect was synergistic after the shorter exposure periods. With longer periods of exposure the effect changed to add i tive. MA of 99% N2 showed complete mortality of S. oryzae after one week and it was 48, 24, 8 and 6 for R. dominica, T. castaneum. active and diapaused larvae of T.granarium, respectively The combined action of DE+ MA of 99% N2 also produced generally enhanced mortalities than each material separately, with all the tested insects. Co-toxicity values of this mixture. indicated potentiation/ or additive effect Synergistic effects were observed after shorter exposure periods with all insects while, additive action was noticed with longer exposure periods.