Abstract:

 【Aim】 To clarify the effects of acquired chlorpyrifos resistance in the predatory mite Neoseiulus barkeri on its biological characteristics, so as to provide a theoretical basis for its field application. 【Methods】 The residual film method was adopted to test the toxicity of chlorpyrifos to N. barkeri in the laboratory, and the lethal medium concentration (LC₅₀) was chosen as the selection pressure. Life table was used to assess the effects of acquired chlorpyrifos resistance on the relative fitness (Rf)of N. barkeri. In addition, Holling type II model was used to analyze the differences in the predation functional response of the chlorpyrifos-susceptible and resistant strains of N. barkeri to eggs and female adults of Panonychus citri at different temperatures.【Results】 A chlorpyrifos-resistant strain of N. barkeri with the resistance ratio of 34.77-fold was obtained after selection of 21 generations. The acquired resistance had no significant effects on the developmental duration, proportion of female offspring and predation functional response of N. barkeri, but shortened the female adult longevity and oviposition period. The susceptible and resistant strains of N. barkeri could not complete the whole generation at 15℃. The fecundity (number of eggs laid per female) of the susceptible and resistant strains of N. barkeri was the highest at 25℃, and the fecundity was significantly higher for the susceptible strain (41.64±1.04 eggs/female) than for the resistant strain (38.80±0.93 eggs/female). Likewise the oviposition periods of the susceptible and resistant strains of N. barkeri were the longest at 25℃, and the oviposition period was significantly longer for the susceptible strain (24.82±1.50 d) than for the resistant strain (21.34±1.26 d). Further, the shortest developmental duration of the susceptible and resistant strains of N. barkeri was recorded at 30℃, being 6.62±0.23 d for the susceptible strain and 6.53±0.13 d for the resistant strain. Meanwhile, the strongest predation ability of the susceptible and resistant strains of N. barkeri to eggs or female adults of P. citri was recorded at 30℃, with the daily maximum predation amounts of the susceptible and resistant strains of N. barkeri to P. citri eggs being 156.25 and 140.85, respectively, and to female adults of P. citri being 23.10 and 22.32, respectively. The relative fitness (Rf) of the resistant strain of N. barkeri was lower than that of the susceptible strain at 25 and 30℃, but slightly higher than that of the susceptible strain at 20 and 35℃. 【Conclusion】 Generally, chlorpyrifos resistance in N. barkeri has little effect on its biological characteristics under different temperatures. The study results provide a theoretical basis for screening resistant strains of N. barkeri and their field application.

Key words: Neoseiulus barkeri, chlorpyrifos, insecticide resistance, fecundity, predation functional response, biological control