The effect of wheat seed coating on Rhyzopertha dominica (F.)and Sitophilus oryzae (L.)
Abstract: The seed coating of wheat was evaluated against adults of the lesser grain borer,Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and the rice weevil, Sitophilus oryzae (L.)(Coleoptera: Curculionidae). Four wheat varieties, Simeto, Saragolla, Canyon and Sculptur weretested; lots of these varieties were treated and the insecticide deltamethrin alone, or incombination with a mixture of the fungicides carboxin and thiram. Adults of the above specieswere introduced in the untreated (control) and the treated quantities, and mortality was evaluatedafter 7, 14 and 21 days of exposure. For R. dominica, mortality was generally low after 7d ofexposure, but it was higher in the treated quantities than in the control. After 14d of exposure,mortality was higher on the seeds treated with the mixture of deltamethrin with the fungicides incomparison with the application of either deltamethrin or the fungicides alone. On the other hand,for S. oryzae, the mixture of deltamethrin with the fungicides caused significantly higher adultmortality even after 7d of exposures, as compared with the treatment of deltamethrin or thefungicides alone. These results indicate a positive additive effect of the two substances, at least inthe case of S. oryzae. At the same time, there were significant differences among the varietiestested. The current results clearly suggest that even fungicides, when used for seed coating, causestored-product beetle mortality. In fact, in some of the cases tested, the use of fungicides canincrease the insecticidal activity of deltamethrin, which is one of the main currently used grainprotectants globally.