Predominantly cell-mediated larvicidal activity of an indigenous Bacillus subtilis F1 strain against lepidopteran...

The present study evaluated the biocontrol potential of soilborne Bacillus strains isolated from the largely unexplored soils of Khyber Pakhtunkhwa, Pakistan, against two globally significant lepidopteran pests, the white-marked tussock moth (Orgyia leucostigma) and the wax moth (Galleria mellonella). Among the isolates screened, Bacillus subtilis F1 exhibited high insecticidal activity, causing 74-77% mortality of larvae within 48 h when treated with whole-cell suspensions. In comparison, treatment with cell-free culture metabolites resulted in moderate mortality (20-23%), indicating that the primary insecticidal effect is largely cell-mediated, with extracellular metabolites contributing a secondary role. While the specific compounds responsible for the metabolite activity were not characterized in this study, previous reports suggested that Bacillus spp. may secrete proteins, enzymes, or secondary metabolites with insecticidal properties, which could explain the observed larval mortality. These findings demonstrated that infection, colonization, or combined cell-associated factors play a major role in larval mortality. To our knowledge, this is the first report of dual larvicidal activity of an indigenous B. subtilis strain against both O. leucostigma and G. mellonella. The present study also highlighted the presence of promising biocontrol agents in underexplored soil ecosystems, supporting their potential application in sustainable insect pest management.

The online version contains supplementary material available at 10.1007/s13205-026-04779-y.