Abstract: Ectropis obliqua nucleopolyhedroviruses (EoNPV) is an effective pathogen of Ectropis obliqua Prout larvae. Ectropis grisescens Warren is a related species of E. obliqua, which is the major pest of tea plant. To investigate the using of EoNPV against E. grisescens, the pathogenic characters of EoNPV on E. grisescens and screening of high efficient strain were studied. The results showed the 1^st instar larvae of E. grisescens was the most sensitive to EoNPV, the mortality was 82.7%-100% infected with EoNPV in the concentration of 2×10⁴-2×10⁸ PIB·mL^-1. The value of LC₅₀ for the 2^nd instar larvae was 2.32×10⁶ PIB·mL^-1 on the 9^th day after inoculation. The virulence of EoNPV against the larvae of 2^nd generation of E. grisescens was highest among the 1^st-5^th generations. The strain QF₄ was screened as high efficient strain through bioassay among all the strains which was extracted from the dead larvae of E. grisescens infected by EoNPV constantly. The mortality rate of E. grisescens infected by this virus strain increased by 51.5% than that of original strain, and the median lethal time was shortened by 1.5 days. Thus it is suggested that the suitable period of spraying in the field could be at the 1^st instar larvae of 2^nd generations and the QF₄ stain could be used to multiply the virus.

Key words: EoNPV, Ectropis grisescens, pathogenic character, high efficient strain