Unravelling the efficacy and reproductive potential of newly discovered entomopathogenic nematodes, Steinernema indicum and Steinernema shori against Spodoptera frugiperda in maize

Abstract

Introduction Spodoptera frugiperda (J.E. Smith), commonly known as the fall armyworm, is one of the most destructive insect pests of maize worldwide, causing substantial economic losses. Its widespread occurrence and increasing resistance to conventional insecticides have intensified the need for effective and sustainable management approaches. Reliance on chemical pesticides not only accelerates resistance development but also poses significant risks to the environment and beneficial non-target organisms. Consequently, environmentally friendly alternatives, particularly biological control strategies, are gaining importance as viable components of integrated pest management programs for this pest. Methods In the present study, the susceptibility of the larval and pupal stages of S. frugiperda to two indigenous entomopathogenic nematode (EPN) species, Steinernema shori NBAIRS80 and Steinernema indicum NBAIRS58, was assessed. The effect of different concentrations of infective juveniles (IJs) of S. indicum and S. shori on their reproductive potential in third-instar S. frugiperda larvae was also investigated under laboratory conditions. Furthermore, the efficacy of S. indicum and S. shori against S. frugiperda was evaluated under both pot and field conditions. Results Results revealed that under laboratory conditions, both EPN species exhibited high virulence against third, fourth, and sixth instar larvae, achieving 100.0% mortality as the concentration increased from 20 to 420 IJs larva-1. However, S. shori caused significantly higher mortality than S. indicum. A similar trend was recorded in pupae, where S. shori caused 81.0% mortality compared to 65.0% by S. indicum. Both species were able to penetrate the larvae and complete their life cycles, producing a higher number of infective juveniles (IJs). However, in both species, penetration declined significantly at higher IJ concentrations. Although emamectin benzoate performed better than both EPN species under both pot and field conditions, S. shori showed improved performance in reducing larval populations after the second round of spraying. Conclusion Considering its effectiveness and environmental safety, the present study highlights the potential of S. shori as a biological control agent against the larval and pupal stages of S. frugiperda. Future studies should evaluate its efficacy against other economically important insect pests and assess its performance under diverse environmental conditions to support its wider field application.