Abstract: 【Objective】Pesticide mixtures can expand controlling spectrum, decrease pesticide dosage and the cost of production, and prolong the service life of insecticides. To a certain extent, nano-emulsion with low energy consumption and good stability can be developed. The effective components of the pesticide can produce biological effects better by pesticide formulation.【Method】Toxicities of fenpropathrin and cyflumetofen (two types of insecticide and acaricide) to Tetranychus cinnabarinus were determined by residual contact vial method. co-toxicity factor was used to evaluate the formulation synergism and co-toxicity coefficient method was adopted to screen the optimum ratio of pesticides, thus a mathematical model equation was fitted by using the method of optimum ratio and co-toxicity coefficient. Based on the optimum ratio, the 8% fenpropathrin·cyflumetofen nano-emulsion was processed by low-energy emulsification method. According to the characteristics of the nano-emulsion and the basic standards formulated by FAO, the quality control indexes of the product was developed. Finally, the performance of the nano-emulsion was primarily determined by the measurements of contact angle and adhesion work.【Result】After 24 h treatment, the LC₅₀ of fenpropathrin and cyflumetofen against T. cinnabarinus female adults was 711.62 and 4.32 mg·L^-1, respectively. Co-toxicity factors method showed that fenpropathrin and cyflumetofen complex had a synergistic effect. Results of the experiment showed that synergism was observed when the ratio of fenpropathrin to cyflumetofen was in range of 18﹕1 to 165﹕1. The synergetic ratio range of fenpropathrin to cyflumetofen is larger and it seems that this pesticide mixtures is feasible. Cotoxicity coefficient method showed the best synergistic effect of fenpropathrin﹕cyflumetofen was 50﹕1, co-toxicity coefficients was up to 209.96. The ratio mathematical model of fenpropathrin﹕cyflumetofen is y=-216.86x²+19201x-424807, R²=0.864, the optimum ratio in theory is 39﹕1, CTC=211.91. Through further cotoxicity coefficient and fitting equation analysis, it showed that toxicity regression equation is y=0.66x+3.8, r=0.9757, LC₅₀=60.96 mg·L^-1, the CTC value is 215.36 as the ratio of fenpropathrin to cyflumetofen was 39﹕1. Finally, this ratio of fenpropathrin to cyflumetofen (39﹕1) was selected as the optimum ratio for preparing nano-emulsion. Through optimization of solvent, emulsifier and water quality, the optimum formula is as follows: fenpropathrin 7.8%, cyflumetofen 0.2%, solvent 10% (ratio of 150# solvent naphtha﹕xylene=4﹕1), emulsifier 9%-11% (ratio of calciumalkylaromaticsulfonate﹕ polyoxyethylene aliphatate=2﹕3), propanetriol 2%, and water up to 100%. The 8% fenpropathrin·cyflumetofen nano-emulsion showed excellent performance, and the 100-fold dilution was pale blue homogeneous translucent liquid system with good dispersity. The experiment of contact angle showed that the 8% fenpropathrin·cyflumetofen nano-emulsion had the smaller contact angle and the 1arger adhesion work which was conducive to the absorption of plant leaves to liquid medicine and thus improve efficacy. 【Conclusion】 Optimal proportions was screened by means of co-toxicity factor, cotoxicity coefficient and fitting equation, which can be more comprehensively and objectively reflect the efficiency of the two compound agents, as well as to provide certain references for pesticide mixtures. It will provide some instructive significance to combined pesticides.

Key words: fenpropathrin, cyflumetofen, Tetranychus cinnabarinus, pesticide mixtures, nano-emulsion, contact angle