Ovicidal, larvicidal and pupicidal activity of the ethyl acetate extracts from soil actinomycetes against tobacco caterpillar, Spodoptera litura (Lepidoptera: Noctuidae)

Actinomycetes are known to produce wide-spectrum of secondary metabolites which has a wide variety of biological activities including insecticidal property. Spodoptera litura is a serious pest that damage various commercial cash crops which directly affects the agricultural productivity. The present study is to isolate soil actinomycetes from the terrestrial soil samples collected from the eastern ghats and screened them with various biological screening methods. There were around 100 actinomycetes isolate were obtained using the serial dilution method. It was subjected to antimicrobial screening using streak method (data not shown) and identified active isolates. The most active seven isolates were identified and their secondary metabolites were extracted using ethyl acetate as solvent. All the seven isolates of ethlyacetae extracts were performed the ovicidal, larvicidal and pupicidal bioassays against agricultural insect pest Spodoptera litura. Based on the calculated LC50 values, the most effective crude extract was found to be Streptomyces Sp. ERI-TVM-055, ethyl acetate extract. It has exhibited 100 % ovicidal activity at lowest LC50 values of 2.3330 ppm and larvicidal activity was exhibited the 100 % at 25.423 ppm of LC50. It also, exhibited the 100 % pupicidal activity at LC50 of 6.273 ppm. Similarly, Streptomyces sp. ERI-TVM-057, ethyl acetate extract exhibited ovicidal activity against S. litura eggs at LC50 of 11.025 ppm. Over all tested all actinomycetes isolate, the most significant isolate is Streptomyces Sp. ERI-TVM-055. The most active extract subjected to GC-MS analysis and the major bio-active molecules were identified. Several compounds present in the crude extract by the study of GC-MS spectrum. The major compounds were identified as Benzene acetic acid (30.19 %) and Acetamide, N-(2- Phenylethyl) (68.37 %) for the insecticidal activity of the active actinomycetes. The present study concluded that Streptomyces Sp. ERI-TVM-055 ethyl acetate extract can be used as microbial pesticides as effective one against agricultural pest S. litura and it leads to identify the active molecules and safe the environments.