Isolation, identification, and virulence of three strains of Beauveria bassiana from silkworms, Bombyx mori

Abstract

Beauveria bassiana (B. bassiana) is a fungus widely used in the production of traditional Chinese medicine Bombyx batryticatus (B. batryticatus) and in the control of agricultural and forestry pests, keeping on discovering new strains with better vitality, virulence and proliferation will be favorable to promote its continuous promotion in production. The aim of this study is to discover and identify new B. bassiana strains from the natural environment of silkworm breeding and to enrich and update its resource base. In the process of preserving the genetic resources of silkworms, we collected a total of 52 B. bassiana samples, and successfully isolated and identified three strains, Bb10B, Bb01J, and Bb01S, through morphological and modern subsystematic evolutionary analyses. The virulence assay showed that strain Bb10B had the highest rate of disease and lethality, with a half lethal time (LT₅₀) of only 6.40 days, and had rapid growth and high spore production. Further studies showed that the virulence of Bb10B against silkworm larvae increased significantly with increasing concentration in the concentration range of 1.2 × 10⁵ to 1.2 × 10⁸ spores/mL, with the median lethal concentration (LC₅₀) of 3.99 × 10⁵ spores/mL. Pathological section analysis of the midgut of silkworms showed that the cells of the midgut of the silkworms were sparsely arranged and locally broken after 4 d of infection. Therefore, this study enriches the germplasm resources of B. bassiana and provides a good basis for promoting its application in B. batryticatus production and pest biological control.