Infectivity of entomopathogenic nematode, Steinernema glaseri on fall army worm (FAW), Spodoptera frugiperda (Smith, 1797) in Maize (Zea Mays)

Abstract

Fall army worm, Spodoptera frugiperda is a major invasive pest of maize crop from Brazil. Entomopathogenic nematode, Steinernema sp. is widely used as a biological control agent against many insect pests. A leaf disc bioassay experiment was conducted to evaluate the efficacy of Steinernema glaseri against all the six instars of fall army worm. Maize leaf discs of approximately 3cm diameter were placed on sterilized Petri plates and sprinkled with a nematode suspension containing infective juveniles of S.glaseri and later fall army worm (FAW) larvae were released. A total of 20 larvae were released per plate and various concentrations of entomopathogenic nematodes viz, 0, 250, 500, 1000 and 2000 infective juveniles per plate were evaluated in five replications for its efficacy against FAW. Insect mortality rate was observed at periodic intervals viz, 24, 48, 72 and 96 hours after nematode inoculation. After 24 hours of inoculation, higher mortality was observed in 1st, 2nd and 3rd instars when compared to 4th, 5th and 6th instar larvae. But uniform mortality was observed after 48 hours of treatment. The highest insect mortality of 100% was observed at 2000 IJ/plate, followed by 95% mortality at 1000 IJ/ plate after 96 hours of nematode inoculation. With increase in the exposure time of FAW larva to S.glaseri, 100% insect mortality was observed in all concentrations evaluated. The infected insect cadavers were then set up in Modified White’s trap to extract freshly multiplied infective juveniles in order to confirm the infectivity of S.glaseri on fall army worm.