Exploring the entomotoxic ability of actinomycetes against Diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae)

Diamondback moth, Pluella xylostella is an important insect pest of cabbage and cauliflower that causes significant yield losses. Several chemicals insecticides are being used by the farmers to manage this pest. Due to indiscriminate usage of insecticides, the minimum residue levels of these chemicals were identified above threshold levels. Therefore, an eco-fiendly approach and naturally available insecticidal compounds were explored in this study. A soil inhibitant actinomycetes bacterial exotoxins were evaluated for their larvicidal activity against P. xylostella . An ethyl acetate extract of 95 actinomycete isolates containing exotoxins was tested against third instar larvae of P. xylostella by leaf disc bioassay method under laboratory conditions. Thirty-two isolates of actinomycete demonstrated entomotoxic nature by achieving larval mortality of > 50%. Isolate AUDT-240 (92%) showed the highest and significant larvicidal activity. The 16S rDNA sequence data of AUDT-240 isolate was matched (99%) with Streptomyces sp. HNGL19 strain. The ethyl acetate extract of AUDT-240 isolate was subjected to Gas Chromatography-Mass Spectroscopy that revealed, three insecticidal (= larvicidal) exotoxins viz ., methyl formate, 3,9-Epoxy-p-mentha-1,8(10) diene and trans-p-mentha-2,8-dienol. In addition to them, two new exotoxins—Cyclohexene, 4-ethenyl-1,4-dimethyl and 2-Cycloxen-1-one, 2-methyl-5-(1-methylethenyl) which were presumed to have insecticidal action. Insecticidal exotoxins from AUDT-240 isolate can be further exploited as a potential microbial based insecticide for eco-friendly management of diamondback moth. Graphic abstract