Insect pests in the rice agroecosystem, particularly the leaf folder, Cnaphalocrosis medinalis (Guenee) and stem borer, Sesamia inferens (Walker), cause significant yield losses. These pests are generally managed by farmers by application of insecticides and a few biocontrol agents. As a component of integrated pest management, biocontrol agents play a dynamic role in pest control. Although diverse microbial communities are available in the rice ecosystem, bacterial genera such as Bacillus and Pseudomonas spp. are broadly used as biocontrol agents. Therefore, an attempt was made to identify other effective entomopathogenic bacteria to manage the above mentioned pests. In this study, the two entomopathogenic bacteria isolated from diseased pink stem borer (S. inferens Walker) larvae collected from rice fields were identified as Skermanella sp. (KX611462) and Serratia sp. (KX761232). The larvicidal activity of these two bacteria was evaluated against third instar larvae of C. medinalis and S. inferens in in vitro assays and on potted rice plants (Oryza sativa var. TN1). The results of this study demonstrated 50% (LC50) larval mortality of C. medinalis at 2.95 × 103 and 5.88 × 103 colony forming units (CFU) ml-1 for Skermanella sp. and Serratia sp., respectively, under in vitro conditions, 2.57 × 104 and 3.38 × 104 CFU ml-1, respectively, in whole plant assays. Similarly, the LC50 value for Skermanella sp. was 3.80 × 104 CFU ml-1 and Serratia sp. was 2.29 × 105 CFU ml-1 for S. inferens larvae. Our study reports the larvicidal activity of Skermanella sp. against C. medinalis and S. inferens.
Keywords: Larvicidal activity; Rice leaf folder; Serratia sp.; Skermanella sp.; Stem borer.
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