Potentiality of native Bacillus thuringiensis isolates against the destructive pest, Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Abstract The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a destructive global pest of cruciferous crops that has evolved resistance to most conventional insecticides, including several Bacillus thuringiensis (Bt) based formulations. The limited diversity of Bt toxins currently deployed has accelerated resistance development, emphasizing the urgent need to identify novel indigenous Bt isolates harboring diverse Cry and vegetative insecticidal protein (Vip) profiles for sustainable resistance management. In the present study, 58 indigenous Bt isolates were screened for the presence of lepidopteran-active toxin genes and toxicity against Plutella xylostella . Polymerase chain reaction (PCR) assays were employed to detect cry1 , cry2 , cry9 , and vip3A genes while protein profiling was performed to evaluate toxin diversity among the isolates. Preliminary screening identified twelve promising isolates, which were further subjected to leaf-disc bioassays at multiple concentrations. Larval mortality data were analysed using probit analysis to estimate median lethal concentrations (LC₅₀) and to assess model fit. Scanning electron microscopy revealed diverse parasporal crystal morphologies, including bipyramidal, cuboidal, and spherical forms. PCR analysis detected cry1 , cry2 , and vip3A genes in several isolates, whereas cry9 was not detected. Protein profiling revealed substantial diversity among the isolates. LC₅₀ values ranged from 0.07 to 0.44 µg mL⁻¹ and were comparable to the reference strain, HD1 (0.06 µg mL⁻¹). Among the isolates, RM12, T20B, and T32 exhibited the highest toxicity against P. xylostella larvae, although their toxicity did not differ significantly from HD1 based on overlapping 95% fiducial limits. The combined occurrence of multiple cry and vip genes, together with diverse protein profiles and crystal morphologies, demonstrates considerable genetic and functional diversity among the indigenous Bt isolates, highlighting their potential for the development of effective Bt-based biopesticides against insecticide-resistant P. xylostella populations.