Effect Of Imidacloprid And Brassinolide Applied On Pepper Seedling Roots On Myzus Persicae(sulzer) And Parasitoid Aphidius Gifuensis

Systemic pesticides can be used in soil to improve the efficacy and avoid direct effect to natural enemies. In this study, a systemic insecuicide, imidacloprid(active ingredient 0, 1, 3, 6 and 12 mg / plant), applied alone or mixed with brassinolide(0.002 mg / plant) by irrigating the pepper seedlings(10-12 leaf stage). The green peach aphid, Myzus persicae Sulzer, infested on pepper plants were monitored at 20, 30, 40 and 50 days after treatment. The relationship between control efficiency and concentrations of imidacloprid and brassinolide was determined. In addition, the optimum proportion of imidacloprid and brassinolide was selected by comparing the related indexes of pepper plants, the green peach aphid, and the parasitoid. Aphidius gifuensis and imidacloprid residues in pepper fruit sixty days after treatment. Thus I determined the optimal application method for management of the green peach aphid and conserve the natural enemy.The results showed that imidacloprid effectively controlled the the green peach aphid population. At the concentration of 6 at the 12 mg imidacloprid treatment. Brassinolide slightly reduced the control efficiency of imidacloprid, especially 50 days after application, and significantly more aphids were found in the treatment of 3 mg imidacloprid plus brassinolide than imidacloprid alone. Application of imidacloprid mixed with brassinolide could promote plant growth. Sixty days after treatment, the plant height and the number of leaves, flowers and fruits were greater than those in the control. Imidacloprid active ingredient detected in pepper leaves was determined by the application dosage of imidacloprid, and it was the highest in the treatment of 12 mg imidacloprid. Meanwhile, active ingredient of imidacloprid in pepper leaves gradually decreased with time prolonged after treatment. Imidacloprid residues in the leaves were lower when application imidacloprid mixed with brassinolide than imidacloprid alone(with an exception at 1 mg/plant). There was a negative correlation(r =-0.695) between aphid population and imidacloprid concentration. Sixty days after treatment, the residues of imidacloprid in pepper fruits that had been treated with 12 mg imidacloprid alone or mixed with brassinolide were only 0.0055 ± 0.0017, 0.0031 ± 0.0001 mg / kg, respectively. There was great weight loss for the green peach aphid and A. gifuensis in the treatment with imidacloprid mixed with brassinolide, however, the weight of A. gifuensis was equivalent to those in control(with an exception of 12 mg/plant). More than 60% of A. gifuensis were emerged in all treatments.In conclusion, imidacloprid(6 mg/plant) effectively controled the green peach aphid on pepper for about 40 days, and the weight of A. gifuensis was equivalent to control. Application of 12 mg/plant imidacloprid could manage the green peach aphid in the whole growth stage until fruit setting, but negatively affected the weight of A. gifuensis. Brassinolide could reduce both the imidacloprid residue in pepper leaves and control efficiency on the aphid, but it has active effect on pepper plant growth and A. gifuensis body weight.