Abstract :
Laboratory and field studies were conducted to evaluate the effect of three inert dusts, diatomaceous earth, kaolin and katelsous as wheat grain protectants against some stored grain Sitophilus oryzae, Rhizopertha domininca and Tribolium confusum. Inert dusts were mixed with wheat grain in the laboratory at different concentrations.The LC50,s of diatomaceous earth, kaolin and katelsous were 0.234, 0.071 and 0.235% w/w, 6.033, 6.306 and 8.938% w/w and 0.495, 0.496 and 103.875% w/w against S. oryzae, R. dominica and T. confusum, respectively one day after treatment. Diatomaceous earth was more effective than the other tested materials as it achieved complete mortality for the three tested insects after two days of treatment at the rate of 0.5% w/w. Results also showed that kaolin and katelsous act slowly on the tested insects, where the higher rates of 8% w/w for kaolin and 0.4% w/w for katelsous gave complete mortality one week post treatment. For the field study (at farmers, storages), the higher concentrations (0.5, 8 and 0.4% w/w) of the three dusts, diatomaceous earth, kaolin and katelsous, respectively were admixed with wheat grain and stored for 6 months at the farms. The results showed that diatomaceous earth gave 100%, 84.4% and 93.3% mortality against the three tested insects, respectively after 6 months of storage at a concentration of 0.5% w/w at 7th day of exposure. Kaolin at 8% w/w showed that adult mortality decreased from 100% at zero time of storage after 5 days of exposure to 10.0%, 5.0% and 15.0% at 6 months of storage after the same period of exposure against the three tested insects, respectively. At zero time of storage, katelsous at a rate of 0.4% w/w showed the percent mortalities of 100%, 100% and 95.7% against the three tested insects, respectively at 5 days of exposure. The residual effect after 6 months of storage decreased to 13.0%, 35.0% and 22.0% mortality against the three insects, respectively at 7 days of exposure. In general, the results obtained showed that the diatomaceous earth was the most effective followed by katelsous and kaolin against the three tested insects. Also, the degree of effectiveness decreased with the increasing of storage periods.
