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Purpose <p>Entomopathogenic nematodes are promising biocontrol agents offering environmentally sustainable alternatives to chemical insecticides. The present study aimed to isolate, identify, and evaluate the bioefficacy of a new <i>Steinernema</i> sp. DA-1 isolate from a forest ecosystem in Bihar, India, with potential application in the management of major lepidopteran pests.</p> Methods <p>A new isolate of <i>S. abbasi</i> was recovered through <i>Galleria</i> baiting from soil samples. Morphological and morphometric analyses were conducted to confirm its identity, followed by molecular characterization using the Internal Transcribed Spacer region marker. Phylogenetic relationships were analyzed to determine genetic divergence from other known <i>S. abbasi</i> isolates. Laboratory bioefficacy assays were conducted against different larval instars (3rd, 4th, and 5th) of <i>Mythimna separata</i> and <i>Spodoptera litura</i>. Average time taken to kill and LD<sub>50</sub> (lethal dose for 50% mortality) values were calculated.</p> Results <p>Morphological, morphometric, and molecular analyses confirmed the identity of the isolate as <i>S. abbasi</i>. Phylogenetic analysis placed it within the <i>S. abbasi</i> clade, showing subtle genetic divergence, indicating local adaptation, except for certain isolates (accession no. KR029837, KR029836, KR029837), which exhibited high divergence. Bioefficacy assays demonstrated significant dose- and age-dependent mortality in both <i>M. separata</i> and <i>S. litura</i>. LD<sub>50</sub> values at 48&#xa0;h post-infection was 30, 35 and 42 infective juveniles (IJs) and 30, 36 and 41 IJs per larva for third, fourth, and fifth instars of <i>M. separata</i> and <i>S. litura</i> respectively. The highest concentration (T5) caused mortality within 28.8&#xa0;h in third-instar larvae, significantly faster compared to lower concentrations.</p> Conclusion <p>This study provides the first validated report of <i>S. abbasi</i> from Bihar, India, revealing its strong virulence against major lepidopteran pests under laboratory conditions. These findings highlight its potential as a biological control agent, warranting further pot and field evaluations before its possible inclusion in regional sustainable pest management programs.</p>

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Characterization and Biocontrol Efficacy of a New Isolate of Steinernema abbasi (Elawad Ahmad & Reid, 1997) Against Spodoptera litura (Fabricius) and Mythimna separata (Walker)

  • 期刊论文

  • 发表日期：

    2025年10月28日

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  • Gurram Mallikarjun,
  • Nishi Keshari,
  • Mohammad Mahboob,
  • H. Jeevan,
  • Sethu Lakshmi,
  • Gummudala Yashaswini,
  • Somala Karthik,
  • M. S. Sai Reddy

摘要

Purpose

Entomopathogenic nematodes are promising biocontrol agents offering environmentally sustainable alternatives to chemical insecticides. The present study aimed to isolate, identify, and evaluate the bioefficacy of a new Steinernema sp. DA-1 isolate from a forest ecosystem in Bihar, India, with potential application in the management of major lepidopteran pests.

Methods

A new isolate of S. abbasi was recovered through Galleria baiting from soil samples. Morphological and morphometric analyses were conducted to confirm its identity, followed by molecular characterization using the Internal Transcribed Spacer region marker. Phylogenetic relationships were analyzed to determine genetic divergence from other known S. abbasi isolates. Laboratory bioefficacy assays were conducted against different larval instars (3rd, 4th, and 5th) of Mythimna separata and Spodoptera litura. Average time taken to kill and LD50 (lethal dose for 50% mortality) values were calculated.

Results

Morphological, morphometric, and molecular analyses confirmed the identity of the isolate as S. abbasi. Phylogenetic analysis placed it within the S. abbasi clade, showing subtle genetic divergence, indicating local adaptation, except for certain isolates (accession no. KR029837, KR029836, KR029837), which exhibited high divergence. Bioefficacy assays demonstrated significant dose- and age-dependent mortality in both M. separata and S. litura. LD50 values at 48 h post-infection was 30, 35 and 42 infective juveniles (IJs) and 30, 36 and 41 IJs per larva for third, fourth, and fifth instars of M. separata and S. litura respectively. The highest concentration (T5) caused mortality within 28.8 h in third-instar larvae, significantly faster compared to lower concentrations.

Conclusion

This study provides the first validated report of S. abbasi from Bihar, India, revealing its strong virulence against major lepidopteran pests under laboratory conditions. These findings highlight its potential as a biological control agent, warranting further pot and field evaluations before its possible inclusion in regional sustainable pest management programs.