Efficacy of imidacloprid mixture with some acaricides in control of melon aphid, Aphis gossypii (Hem.: Aphididae) under laboratory conditions

The use of pesticide mixtures is one of the effective ways to reduce spraying costs, reduce their consumption and prevent resistance development in the pest’s population. However, due to the potential hazards, before any recommendation to mix pesticides, the need for mixing and its physical and chemical compatibility should be carefully considered. In this study, due to the synchronicity of aphid control with acari pests, the insecticidal performance of mixtures of imidacloprid (SC 35%) with fenpyroximate (SC 5%), spirodiclofen (SC 24%) and etoxazole (EC 10%) were investigated on third instar nymphs of melon aphid, A. gossypii. Furthermore, the activity levels of detoxifying enzymes esterase and glutathione S-transferase was measured in treated insects with these compounds. Bioassay tests were performed with a Potter spray tower method. LC50 value of the imidacloprid alone and in combination with each of the acaricides of fenpyroximate, spirodiclofen and etoxazole were 45.41, 84.91, 44.65 and 48.94 mg/l, respectively. In addition, by estimating the Combination Index (CI), a synergistic effect was observed in the mixture of imidacloprid with each of the acaricides and the highest synergistic activity occurred at concentrations higher than LC30. In mixed treatments, the CI index decreased with increasing concentration. The results of detoxifying enzyme activities showed that the activity levels in mixture of imidacloprid: fenpyroximate and imidacloprid: spirodiclofen were higher than that of imidaloprid alone and mixture of imidacloprid: etoxazol. In this study, the lowest CI index at LC50 concentration, were for binary mixture of imidacloprid: etoxazol (0.529) and imidacloprid: spirodiclofen (0.545) that exhibited high synergistic effect. The results of this study showed that the effectivness of imidacloprid (SC) was increased for control melon aphid, when mixed with the tested acaricides. However, the mixture of imidacloprid: etoxazole showed the highest insecticidal performance.