Abstract
The application of the new method for calculating the synergism and potentiation percentage of Milkthistle plant oil (Silybum mariamum L.) and Piperonyl butoxide which used as an activator to increase the toxicity of deltamethrin 2.5% EC. against Tribolium confusum Duval, showed that the activation percentage piperonyl butoxide to Deltamethrin reached 2.8, and this activation was by synergism only because piperonyl butoxide is not toxic, while the total activation percentage to deltamethrin produced by Milkthistle oil reached 3.12, and the synergism percentage from total activation percentage reached 2.85 and the potentiation reached 0.27. The previous results proved that calculating the synergism of toxic activator compound by using Metcalf equation is not correct because it calculate the total activation instead of synergism percentage .
