Effects of diatomaceous earth on the mortality and progeny production of Rhyzopertha dominica (Coleoptera: Bostrychidae

Abstract

Laboratory experiments were conducted to assess the insecticidal effect of the diatomaceous earth (DE) formulation Insecto ® against adult stage of Rhyzopertha dominica (F.) at two levels of relative humidity i.e. 40 and 55%, and three exposure periods of 7, 14, and 21 days . Test insects were placed in vials containing 40 g of soft winter wheat mixed with 0.25, 0.50, 1.00, 1.50 and 2.00 g kg -1 DE. After respective exposure periods, mortality in all dose rates except 0.25 and 0.50 g kg -1 was found to be significantly different from mortality in control. After each exposure interval, dead and live insects were counted and removed, and then the vial containing wheat was returned to corresponding humidity chamber for 8 weeks until F 1 adults emerged. For F 1 production, applications at all dose rates were significantly different from control group. Mortality regardless of dosage for 7, 14 and 21 days exposure intervals were between 27.67– 33.40 %. Despite the fact that mortality increased with the increasing dose rate, total mortality was not obtained even at the highest rate of DE. F 1 production decreased with the increasing dose rates for both r.h. conditions. Containment of population was achieved at 1.50 g kg -1 of DE for 7 days of exposure period and at 2.00 g kg -1 of DE for 14 and 21 days of exposure periods . For each exposure intervals, F 1 production of R. dominica decreased with the increasing dose rates of DE. Mortality regardless of exposure interval was 59% at 1.50 g kg -1 of DE and 75% at 2.00 g kg -1 of DE.