Abstract
BackgroundSpodoptera litura (Fab.) (Lepidoptera: Noctuidae) is a serious agricultural pest that infests many commercially important crops of Southeast Asian countries. Indiscriminate use of chemical pesticides has led to various health hazards as well as insecticide resistance. Entomopathogenic fungi (EPF) provide an important alternative as biological control agents. Metarhizium rileyi is an EPF with a specific host range for lepidopteran pests. The present study aimed to identify virulent M. rileyi isolate against S. litura larvae and analyse their extracellular cuticle-degrading enzyme activities.ResultsThree M. rileyi isolates viz M. rileyi NIPHM, M. rileyi MTCC 4254 and M. rileyi MTCC 10395 formulations were evaluated at different concentrations against 2nd instar larvae of S. litura. A maximum percent mortality of 63.33% was recorded in M. rileyi NIPHM (12 g/l), followed by M. rileyi MTCC 4254 (58.33%) at the same concentration, 10 days post-treatment. Maximum means of chitinase, protease and lipase activities (0.44, 1.58 and 2.95 U/ml, respectively) were recorded in the case of M. rileyi NIPHM. Correlation analysis was positive between enzyme activity and larval mortality.ConclusionsMetarhizium rileyi NIPHM recorded the highest enzymatic activity and exhibited the maximum mortality rate against 2nd instar larvae of S. litura, suggesting the possible role of these enzymes in the pathogenicity of the fungus. Further knowledge in this regard may help in the development of enzyme-based screening methods for selecting virulent fungal isolates for the eco-friendly management of crop pests.
Highlights
Spodoptera litura (Fab.) (Lepidoptera: Noctuidae) is a serious agricultural pest that infests many commercially important crops of Southeast Asian countries
Virulence of various Entomopathogenic fungi (EPF) may be associated with cuticle-degrading enzymes that are considered important in the infection process
Fungal isolates Two fungal isolates viz M. rileyi Microbial Type Culture Collection and Gene Bank (MTCC) 4254 and MTCC 10395, procured from the Institute of Microbial Technology (IMTECH), Chandigarh, India, and one M. rileyi NIPHM isolate procured from the National Institute of Plant Health Management (NIPHM), Hyderabad, India, were used in the present study
Summary
Spodoptera litura (Fab.) (Lepidoptera: Noctuidae) is a serious agricultural pest that infests many commercially important crops of Southeast Asian countries. The present study aimed to identify virulent M. rileyi isolate against S. litura larvae and analyse their extracellular cuticle-degrading enzyme activities. The fungus Metarhizium rileyi (Farlow) Kepler, S.A. Rehner and Humber, formerly known as Nomuraea rileyi (Kepler et al 2014), is an EPF that has been studied as an alternative method for the management of lepidopteran pests belonging to different genera (Boucias et al 1982). Virulence of various EPF may be associated with cuticle-degrading enzymes that are considered important in the infection process. The present study was undertaken to evaluate the extracellular enzymatic activities and pathogenicity of different M. rileyi isolates against S. litura so as to identify virulent M. rileyi isolate for S. litura management
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