Analysis of Joint Action of Insecticides Against House Flies

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Abstract
To analyze the joint action of two (or more) insecticides, the actual toxicity indexes of the components and their mixture are determined by dosage-mortality curves. The theoretical toxicity of the same mixture is equal to the sum of toxicity indexes calculated from the percentage of each component times its respective toxicity index. Therefore, the joint toxicity or Co-toxicity coefficient of a mixture A coefficient of a mixture near 100 indicates probability of similar action; independent action usually should give a coefficient less than 100, while a coefficient significantly above 100 strongly indicates synergism. Toxicity significantly less than that of the strongest toxicant alone shows antagonism. Thirty-nine mixtures each containing two to four insecticides were tested against the house fly (Musca domestica L.) and their results were calculated by this method. Generally, chemically related compounds gave similar action, while unrelated compounds gave independent action. 3-(Dimethoxyphosphinyloxy)-N,N-dimethyl-crotonamide (SD 3562)and sesamex showed high synergistic action. However, a mixture of methyl parathion and sesamex indicated significant antagonism.