关键词: 根虫瘟霉, 小菜蛾, 时间剂量死亡率模拟, 毒力, 虫瘟霉症

Abstract: Four Zoophthora radicans (Entomophthorales) isolates from different hosts were bioassayed against the second instar larvae of the diamondback moth, Plutella xylostella in the laboratory. Each isolate included eight dosages resulting from spore showers at different times. On day 8 after exposure to a spore shower for Inoculation, a P. xylostella derived isolate, ARSEF1100, caused a cumulative mortality of 2.38%－97.44% at 0.53－319.32 conidia/mm² with all cadavers exhibiting typical Zoophthora syndrome. Two isolates derived from Empoasca, ARSEF2699 and F99101, killed 2.38%－50.00% and 2.38%－57.89% at 1.56－314.84 and 1.84－484.08 conidia/mm², respectively, whereas the isolate ARSEF1342 from Pieris brassicae，killed only 6.52%－13.63% at 3.54－633.40 conidia/mm². Typical Zoophthora syndrome was observed only in approximately one third of cadavers killed by the latter three isolates. Fitting the data to a time-dose-mortality model generated the estimates of parameters for time and dose effects of each isolate. The parameter estimates for dose effect (β) was 1.89 for ARSEF1100, 1.48 for F99101, 1.23 for ARSEF2699, and 0.37 for ARSEF1342, which are significantly different. The LD₅₀ values estimated for ARSEF1100 were 231.68，113.08, 71.41, 40.87 and 35.30 conidia/mm² on days 4－8 after exposure, respectively. The corresponding estimates were 1 344.43，922.39，555.58，410.06 and 397.07 conidia/mm² for ARSEF2699, and 666.86，451.64，413.82，350.65 and 332.57 conidia/mm² for F99101. The virulence for ARSEF1342 was too weak for its LD₅₀ to be estimated. The isolate ARSEF1100 was the most virulent to P. xylostella, and can be considered as a microbial agent for control of the pest.

Key words: Zoophthora radicans, Plutella xylostella, timedosemortality modeling, virulence, typical Zoophthora syndrome