Insecticidal activity of Iranian diatomaceous earth, alone or in combination with Mentha longifolia plant extract to control Rhyzopertha dominica adults on different cereals

Storage insect pests cause considerable damage to grains every year, and reduce quantitative and qualitative value of stored products. One of the most important problems of controlling storage pests with chemical pesticides is occurrence of resistant to these pesticides, residues remaining on food products and endangering the health of the environment and other living beings. Diatomaceous earth has been introduced as a suitable alternative to chemical insecticides and can be used as one of the parts of integrated pest control programs. In this study, the insecticidal effect of different formulations of diatomaceous earth was evaluated against the lesser grain borer, Rhyzoperta dominica F. (Coleptera: Bostrychidae) adults in different grains including wheat, barley, rice, paddy and corn. Cereal grains were treated with a concentration of 400 ppm of a commercial formulation, Silicosec®, Iranian DE formulation Dryasil alone, Dryasil + 0.05% plant extract (Mentha longifolia L.), talcum powder + 0.05% M. longifolia extract. The insects’ mortality was counted 1, 5, 7, 10 and 14 days after treatment. The Dryasil formulation and Silicosec® were significantly controlled the populations of tested insects in the grain mass. The mean mortality percentage of R. dominica in wheat, barley, rice, paddy and corn treated with Silicosec® were 53.3, 98.8, 44.4, 60.0 and 68.8%, respectively, 14 days after treatment. While the Iranian formulation of diatomaceous earth was able to control 50.0, 91.1, 60.0, 58.8 and 67.2 % of R. dominica adults, respectively. The insecticidal effect of diatomaceous earth increased over time. The lowest LT50 value was reported in barley, which indicated greater protection of this product than other cereals. In barley, Silicosec®, Dryasil, and Dryasil + M. longifolia extract caused 50% mortality on R. dominica adults after 3.06, 5.39, and 9.01 days, respectively.