Fall armyworm (FAW) Spodoptera frugiperda (J.E. Smith) Lepidoptera: Noctuidae is an invasive polyphagous pest that causes severe damage to several agricultural crops. The use of pesticides is limited because of their mode of feeding and resistant development. Hence, the present work aimed to determine the pathogenicity of entomopathogenic bacteria (Bacillus spp.) against FAW in terms of mortality and growth inhibition. In this study, initially 49 native Bacillus isolates, isolated from diverse habitats in India, along with five reference strains, were screened for their efficacy against neonates of S. frugiperda under controlled laboratory conditions, followed by virulence and combinatorial bioassays. Five native Bacillus isolates (VKK1, VKK5, S16C2, S25C1, and SOIL 20) showed mortality in the range of 35.49–65.52% against neonates of S. frugiperda at single concentration (1000 μg g−1 of diet). These five isolates, along with one reference strain Btk-HD1 (Bacillus thuringiensis serovar kurstaki strain HD1), were further tested to find the median lethal concentration (LC50) for neonates of S. frugiperda. Among these, native Bt strain VKK5 showed the lowest LC50 (718.40 µg/g of diet) and HD1 showed the highest LC50 (3352 µg/g of diet). Combinatorial bioassay against neonate and third instar larvae showed that the combination of VKK5 and VKK1 had an additive effect. Moreover, growth inhibition was also recorded. The combination of Bt strains leads to an enhancement of pathogenicity toward FAW larvae at the initial stage of development, and in later stages, it affects their growth and development. Thus, biocontrol of FAW by entomopathogenic bacteria (Bt) can play a vital role in the effective management of FAW.

中文翻译：

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天然芽孢杆菌分离株单独和组合对抗秋粘虫、草地贪夜蛾不同幼虫龄的功效

秋粘虫 (FAW) 草地贪夜蛾 (JE Smith) 鳞翅目：夜蛾科是一种入侵性多食性害虫，对多种农作物造成严重损害。由于其取食方式和抗药性的发展，农药的使用受到限制。因此，目前的工作旨在确定昆虫病原菌（芽孢杆菌属）对秋粘虫的死亡率和生长抑制的致病性。在这项研究中，首先在受控实验室条件下筛选了从印度不同栖息地分离的 49 种本地芽孢杆菌分离株以及 5 种参考菌株，以确定它们对草地贪夜蛾新生儿的功效，然后进行毒力和组合生物测定。五种天然芽孢杆菌分离株（VKK1、VKK5、S16C2、S25C1 和 SOIL 20）在单一浓度（1000 μg g−1 饮食）下对草地贪夜蛾新生儿的死亡率在 35.49–65.52% 范围内。对这五种分离株以及一种参考菌株 Btk-HD1（苏云金芽孢杆菌库斯塔基菌株 HD1）进行了进一步测试，以找出草地贪夜蛾新生儿的半数致死浓度 (LC50)。其中，天然 Bt 菌株 VKK5 显示最低 LC50（718.40 µg/g 饮食），HD1 显示最高 LC50（3352 µg/g 饮食）。针对新生和三龄幼虫的组合生物测定表明，VKK5 和 VKK1 的组合具有累加效应。此外，还记录了生长抑制。Bt菌株的组合导致对草地贪夜蛾幼虫在发育初期的致病力增强，并在后期影响其生长发育。因此，昆虫病原菌（Bt）对草地贪夜蛾的生物防治在草地贪夜蛾的有效管理中发挥着至关重要的作用。