Synergistic Effects of Amitraz on Imidacloprid and Malathion against Cotton Aphid, Aphis gossypii (Hem: Aphididae)

For more than a century, chemical insecticides have been the most primary tool used by growers to control the cotton aphid, Aphis gossypii, as an important polyphagous pest worldwide. The application of insecticide mixtures through different modes of action is currently favored for resistance management of this pest. In this study, the synergistic interactions between amitraz with each of the two commonly used insecticides, i.e. imidacloprid and malathion, were studied using A. gossypii as target pest. The effects of amitraz combination on the activity of three detoxifying enzymes of cotton aphids were then evaluated using physiological assays. The synergistic effects of amitraz on imidacloprid were observed at all Lethal Concentrations (LC۱۰-LC۹۰), while, for malathion it was observed at concentrations higher than LC۳۰. The highest synergist ratio in the mixture of amitraz with malathion (LC۹۰) and imidacloprid (LC۱۰) was ۱.۵ and ۳.۰۹, respectively. The inhibition of Glutathione S-Transferase (GST) activity seems to be the main reason for amitraz to impose its synergistic effects.