Efficacy of secondary metabolites of promising entomopathogenic actinomycetes against fall armyworm, Spodoptera frugiperda (Lepidoptera : Noctuidae)

Biopesticides are the most reliable strategies to protect crops at the initial stages of pest attack. The present investigation was conducted to identify effective entomopathogenic actinomycetes for management of Fall Armyworm (FAW). Of 24 actinomycetes that were previously screened against 2nd instar larvae of FAW, three isolates were identified as effective, viz., KG-13, CAI-134 (Nocardiopsis sp.), and CAI-17 (Streptomyces albus) which showed mortality more than 50 %. These three promising isolates were selected for further evaluation using their Intracellular Metabolites (ICM) and Extracellular Metabolites (ECM) in both laboratory and greenhouse conditions. Under laboratory through diet impregnation bioassay, KG-13 caused maximum mortality in 2nd instar larvae of FAW, with both ECM (85.19%) and ICM (70.37%). Larval prolongation (22.57 ± 1.98 days) and larval pupal intermediates were observed in the ECM of CAI-17. In the evaluation of chitinase activity, the highest zone of inhibition was recorded in KG-13 (34.67 mm), followed by CAI-17 (25.33 mm) and CAI- 134 (19.67 mm). ECM of KG-13, CAI-17 and ICM of KG-13 were noticed with 66.66, 53.33 and 53.3 % mortality in greenhouse studies. This study shows the impact of promising actinomycetes secondary metabolites on the 2nd instar FAW and their effectiveness in both laboratory and greenhouse conditions. Comparatively, less mortality was noticed in the greenhouse than in laboratory conditions, whereas Bt var. kurstaki (73.33%) and Emamectin (73.33%) in greenhouse studies showed considerablemortality than actinomycetes metabolites.