金龟子绿僵菌对斜纹夜蛾幼虫的生防效果、抗氧化酶活性和肠道细菌群落的影响

【目的】测定金龟子绿僵菌(Metarhizium anisopliae)对斜纹夜蛾(Spodoptera litura) 2龄幼虫的毒力,研究金龟子绿僵菌侵染后寄主体内抗氧化酶活性和肠道内细菌群落的变化,探讨斜纹夜蛾对金龟子绿僵菌侵染的防御机制。【方法】采用浸渍法测定不同浓度金龟子绿僵菌对斜纹夜蛾2龄幼虫的毒力;应用IlluminaMiSeq高通量测序技术测定肠道细菌群落。【结果】不同浓度的孢悬液对斜纹夜蛾2龄幼虫均有一定的毒力,处理7 d时半致死浓度(LC_(50))为3.944 107个孢子/mL;浓度为1.0×10~9个孢子/mL时,半致死时间最短(LT_(50))为4.6 d,校正后的死亡率为81.03%。处理后未致死的斜纹夜蛾幼虫体内抗氧化酶活性显著高于对照组。处理后致死的斜纹夜蛾幼虫肠道细菌群落多样性显著高于对照组;且处理后致死的斜纹夜蛾幼虫肠道细菌群落组成与对照组差异显著。【结论】金龟子绿僵菌对斜纹夜蛾幼虫的致死率和致死效率与金龟子绿僵菌的浓度呈正相关;斜纹夜蛾幼虫体内的抗氧化酶可能在抵抗金龟子绿僵菌侵染的过程中起重要作用。金龟子绿僵菌的侵染会导致斜纹夜蛾幼虫肠道细菌群落多样性升高和组成发生变化,Enterococcus、Escherichia和Pseudomonas等属可能是影响斜纹夜蛾幼虫抵抗金龟子绿僵菌侵染致死的重要因素。

Biocontrol of Spodoptera litura larvae by Metarhizium anisopliae

Objective] (a) To determine the virulence of Metarhizium anisopliae to the second instar larvae of Spodoptera litura, (b) To investigate the response of the intestinal bacterial community and antioxidant enzyme to the infection of M. anisopliae, and (c) to explore the defense mechanisms of S. litura against M. anisopliae. Methods] The toxicity of different concentration of M. anisopliae against 2^nd instar larvae of S. litura was tested by Dipping method. The intestinal bacterial community was determined by Illumina MiSeq high-throughput sequencing of 16S rDNA amplicons. Results] Different concentrations of spore suspension had virulence to the 2^nd instar larvae of S. litura. After 7 days of treatment, the half lethal concentration (LC₅₀) was 3.944×10⁷ spores/mL. The 1.0×10⁹ spores/mL treatment had the fastest half lethal time (LT₅₀) of 4.6 d, with a corrected lethal rate of 81.03%. Antioxidant enzyme activities were significantly higher in the treated alive larvae compared with that in the control group. The intestinal bacterial community diversity of lethal S. litura larvae was significantly higher than that of the control group, and the bacterial community composition differed significantly between the lethal and control group. Conclusion] The mortality rate and lethal efficiency of M. anisopliae against S. litura larvae were positively correlated with the concentration of M. anisopliae. The antioxidant enzyme in S. litura larvae may play important roles in resisting the infection of M. anisopliae. The infection of M. anisopliae leads to increase of diversity and change of composition of the intestinal bacterial community of S. litura larvae. Genera, such as Enterococcus, Escherichia and Pseudomonas, may be important factors affecting the mortality of S. litura larvae against infection of M. anisopliae.