玫烟色拟青霉对小菜蛾致病力的时间-剂量-死亡率模型模拟

小菜蛾Plutella xylostella是我国南方十字花科蔬菜上的重要害虫,已对田间常用的化学杀虫剂产生了严重的抗性。为寻找有效的小菜蛾生物防治措施,本实验研究了一株分离自家白蚁的玫烟色拟青霉Paecilomyces fumosoroseus (SCAU-PFCF01)对小菜蛾2～4龄幼虫的致病力。实验采用浸液法,供试浓度为1×10³、1×10⁴、1×10⁵、1×10⁶和1×10⁷个孢子/mL。结果表明：随玫烟色拟青霉孢子浓度的升高,小菜蛾的感病死亡率增加,在浓度为1×10⁷ /mL时,小菜蛾2、3和4龄幼虫的累计死亡率分别为96%、85%和80%。玫烟色拟青霉对小菜蛾各龄幼虫的致病力与供试龄期有关,其感病的敏感顺序为2龄、3龄和4龄。用时间 剂量 死亡率模型（time-dose-mortality model,TDM）对各龄幼虫的致病力数据进行模拟,所建模型均顺利通过Hosmer-Lemeshow拟合异质性检验,表明模型拟合良好,并由模型估计出了该菌株对小菜蛾各龄幼虫的致死剂量与致死时间。2龄幼虫接种后第7天、3龄幼虫接种后第5天、4龄幼虫接种后第4天的LC₅₀估计值分别为1.17×10⁴、1.44×10⁴和5.21×10⁴ /mL,LC₉₀估计值分别为1.98×10⁶、3.82×10⁷和1.29×10⁸ /mL。玫烟色拟青霉对小菜蛾幼虫的致死时间与浓度相关,供试各龄幼虫的LT₅₀值随着孢子悬浮液浓度的增加而递减,在1×10⁵～1×10⁷ /mL的范围内,2龄幼虫的LT₅₀值从3.16天降低到1.72天,3龄幼虫的LT₅₀从3.21天降低到1.83天,4龄幼虫的LT₅₀从3.69天降低到2.04天。即2龄幼虫致死所需的时间最短,其次为3龄幼虫,4龄幼虫致死所需的时间最长。结果显示了该株玫烟色拟青霉在小菜蛾的生物防治中具较强的应用潜力。

The time-dose-mortality model of a Paecilomyces fumosoroseus isolate on the diamondback moth,Plutella xylostella

The diamondback moth, Plutella xylostella, is an important insect pest of cruciferous vegetables in south China and has developed serious resistance to insecticides used. In an effort to search for alternative control methods, the pathogenicity of an isolate (SCAU-PFCF01) of the fungus Paecilomyces fumosoroseus, originally derived from Coptotermes formosanus, against the diamondback moth larvae, was studied in the laboratory by immersing larvae of different instars into serial concentrations of 10³－10⁷ conidia/mL of the fungus. The mortality of the diamondback moth caused by infection of P. fumosoroseus increased with the concentration of conidial suspension and the time after treatment. The highest concentration (10⁷ conidias/mL) treatment caused 96%, 85%, and 80% mortality for 2nd, 3rd, and 4th instar larvae on day 7, respectively. A time-dose-mortality model was used to analyze the bioassay data and the model fitted the data well, resulting in parameters for estimating the time and dose effects. The pathogenicity of P. fumosoroseus to the diamondback moth differed among various larval stages. The susceptibility of the diamondback moth larvae to P. fumosoroseus decreased in the sequence of 2nd instar, 3rd instar, and 4th instar. The estimated LC₅₀ values of 2nd instar on day 7 after treatment, 3rd instar on day 5 after treatment and 4th instar on day 4 after treatment were 1.17×10⁴, 1.44×10⁴, and 5.21×10⁴ conidia/mL, respectively; while LC₉₀ of 2nd, 3rd, 4th instar larvae were 1.98×10⁶, 3.82×10⁷, and 1.29×10⁸ conidia/mL, respectively. The median lethal time of P. fumosoroseus to the diamondback moth larvae differed at various concentrations. Values of LT₅₀ of all tested instars were shortened with concentration. The LT₅₀ values of 2nd, 3rd, and 4th instar were 3.16-1.72 days, 3.21-1.83 days and 3.69-2.04 days, respectively, in the range of 1×10⁵－1×10⁷ conidia/mL. The results suggested the potential of the isolate SCAU-PFCF01 for use in microbial control of P. xylostella.