The efficacy of two diatomaceous earths on the mortality of Rhyzopertha dominica and Sitophilus oryzae

The insecticidal activity of two commercial formulations of diatomaceous earths (DEs) was evaluated in the laboratory against two major pests of stored grain: Rhyzopertha dominica (F.) (Coleoptera Bostrichidae) and Sitophilus oryzae (L.) (Coleoptera Curculionidae). The formulations Protector(R) and SilicoSec(R) were tested at two different doses (500 and 1000 ppm) against adults of the two species. Bioassays were carried out using 2-liter-glass jars containing common wheat (with a moisture content ranging from 10.5 to 11.7%, for R. dominica, and 10.7 to 13.4% for S. oryzae) mixed with the DEs, and maintained at 26.7 degree C and 60% RH. The efficacy of the treatment was evaluated by recording adult mortality after 2, 7 and 14 days. Both formulations have shown an adulticidal effect, although the mortality was influenced by species, dosages and exposure time. Protector(R) showed a significant insecticidal activity against the lesser grain borer and the rice weevil already after two days of treatment. After 14 days the mean mortality was greater than 95% even at a dosage of 500 ppm for R. dominica, and greater than 87 and 92% at a dosage of 500 ppm and 1000 ppm respectively, for S. oryzae. SilicoSec(R) caused less mortality than Protector(R) after 2 days of exposure, especially for the S. oryzae. However, there was no difference between formulations after 7 or 14 days.