Abstract: The response of the green peach aphid,Myzus persicae,to low sublethal concentrations of imidacloprid (0.01～1.0 μg·ml^-1) sprayed by an electronic sprayer was assessed at the regime of 23℃ and 12:12(L:D) during a 7-day period.The resultant data were fitted to time-concentration-mortality model,generating estimates of lethal concentrations (LCs) and lethal times (LTs) that depended on each other at an expected efficacy level.On days 1 and 5 after spray,for instance,the LC₅₀ with 95% confidential limits were estimated as 2.8(1.8～4.6) and 0.5(0.4～0.6)μg·ml^-1,LC₉₀ 7.1(3.8～13.0) and 1.2(1.0～1.5),and LC₉₉ 11.9(6.0～23.9) and 2.0(1.5～2.8),respectively.At the concentrations of 1.0,2.0 and 3.0 μg·ml^-1,the LT₅₀ estimates were 2.9,1.4,and 1.0 days,respectively;and LT₉₀ 5.8,3.6,and 2.4 days.The results indicate that the fast knockdown concentration of imidacloprid commonly recommended for field spray in aphid control(～33 μg·ml^-1) was even higher than the upper limit of its LC₉₉ within 24 h.Based on the above response of M.persicae to the low sublethal concentrations sprayed,the application rate of imidacloprid for an expected efficacy level against aphids could be greatly decreased if a longer period of action time was allowed.A discussion was given on more rational application of imidacloprid in relation to relief of aphid resistance to the chemical insecticide and its potential to stimulate fertility of spider mites.

Key words: Myzus persicae, Imidacloprid, Low sublethal sprays, Bioassay, Time-concentration-mortality modeling