继代培养球孢白僵菌对斜纹夜蛾幼虫毒力和产孢量的影响及菌株复壮研究

【目的】明确球孢白僵菌(Beauveria bassiana)在连续继代培养过程中对斜纹夜蛾(Spodoptera litura)二龄幼虫毒力、产孢量的影响，并进行菌种复壮研究，为进一步利用球孢白僵菌对斜纹夜蛾的生物防治提供参考。【方法】将球孢白僵菌SCAUJH19继代培养10代，得到F₁～F₁₀代菌株并测定产孢量。采用浸虫法分别用F₁～F₁₀代菌株处理斜纹夜蛾二龄幼虫，测定其对斜纹夜蛾二龄幼虫的毒力；建立模型分析球孢白僵菌继代培养代数、毒力与产孢量的关系及毒力退化规律。采用活虫复壮法对F₄、F₆、F₈、F₁₀代菌株进行复壮，比较复壮前后对斜纹夜蛾二龄幼虫的毒力效果，并测定产孢量。【结果】球孢白僵菌F₁～F₅代菌株对二龄斜纹夜蛾幼虫毒力无显著差异，处理7 d时校正死亡率为42.44%～45.22%，而F₆、F₈、F_1...

Influence of Subculture of Beauveria bassiana on Virulence and Spore Production of Spodoptera litura Larvae and its Strain Rejuvenation

【Objective】The study aimed to investigate the impact of continuous subculture of Beauveria bassiana on the virulence and spore production of second-instar larvae of Spodoptera litura. Additionally, a study on strain rejuvenation was conducted to offer references for the biological control of B. bassiana against S. litura.【Method】The primary strain, designated as F0 (SCAUJH19), was inoculated on PDA medium, and subsequent generations (F1~F10) were obtained through ten consecutive subcultures. The second-instar larvae of S. litura were exposed to 1×108 CFU/mL B. bassiana treatment by insect dipping method. The virulence of different sub-cultured strains against second-instar larvae was determined, and spore production for each generation was quantified. A model was constructed to analyze the relationship between virulence, spore production and successive subcultures in B. bassiana strains and laws of virulence degeneration. Live insect rejuvenation method was implemented on strains from generations F4, F6, F8 and F10, followed by a comprehensive comparison and analysis of the virulence effects on second-instar larvae before and after rejuvenation, along with measuring their spore productions.【Result】No significant difference in virulence was observed among F1~F5 subcultures of B. bassiana strains, with mortality rates ranging from 42% to 45% when treat for 7 d. However, the mortality rate of F6, F8 and F10 strains against S. litura decreased to 37%, 22.94% and 12.17%. Spore production analysis indicated that F1~F5 strains maintained a spore quantity of above 9.65~10.43×108 CFU/mL, whereas spore quantities of F6, F8 and F10-generation strains decreased to 7.62×108 CFU/mL, 5.14×108 CFU/mL and 4.69×108 CFU/mL. The constructed model revealed an exponential decrease in spore production with subcultures from the F5 generation, with a positive correlation between spore production and virulence. Strains with fewer subculture generations exhibited higher spore production and greater pathogenicity to second-instar larvae of S. litura. After the rejuvenation of F4, F6, F8 and F10 strains with live insect rejuvenation method, the corrected mortality of the treated strains of S. litura second-instar larvae remained above 50%, surpassing the highest mortality of the original strains, and the spore production of the rejuvenated strains exceeded that of the pre-rejuvenated strains.【Conclusion】After 4 to 5 generations of subculture, B. bassiana demonstrates a gradual decrease in spore production and virulence against second-instar larvae of S. litura and strain rejuvenation is needed. The sub-generation of B. bassiana could be effectively restored or improved to its original characteristics through the live insect rejuvenation method. Spore production of the same strain can be served as a valuable reference index for evaluating its virulence.