不同寄主来源的根虫瘟霉菌株对小菜蛾幼虫的毒力比较

在不同寄主来源的4株根虫瘟霉Zoophthora radicans对小菜蛾 Plutella xylostella 2龄幼虫的生物测定中，发现源于小菜蛾的菌株ARSEF1100毒力最强，在0.53～319.32/mm²的孢子剂量下，接种后第8 天累计死亡率为2.38%～97.44%，虫尸全部表现典型的虫瘟霉症状；源于叶蝉的ARSEF2699和F99101菌株的同日累计死亡率分别为2.38%～50.00% (剂量为1.56～314.84/mm²孢子)和2.38%～57.89% (剂量为1.84～484.08/mm²的孢子)；而源于菜粉蝶的ARSEF1342菌株在3.54～633.0/mm²的孢子剂量下只引发6.52%～13.63%的累计死亡率，后3个菌株致死的小菜蛾幼虫仅部分表现典型症状。所获数据经时间剂量-死亡率模型模拟分析，剂量效应参数依次为ARSEF1100 (1.89) > F99101 (1.48) > ARSEF2699 (1.23) > ARSEF1342 (0.37)，相互间差异均达极显著水平。接种后4～8 天内，ARSEF1100的LD₅₀值分别为231.68、113.08、71.41、40.87和35.30/mm²的孢子，其毒力远高于其余3个菌株；ARSEF2699的相应LD₅₀值为1344.43、922.39、555.58、410.06和397.07/mm²的孢子；F99101的LD₅₀值为666.86、451.64、413.82、350.65和332.57/mm²的孢子，而ARSEF1342的毒力太弱难以估计。这些结果表明，ARSEF1100菌株最有希望用于小菜蛾的微生物防治。

Comparative virulence of Zoophthora radicans isolates from different hosts against Plutella xylostella larvae

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.