Infectivity of Local Strains of the Insect Pathogen Nomuraea Rrleyi to Fall Armyworm, Spodoptera frugiperda

Larvae of Lepidoptera cause heavy losses in agriculture worldwide. The fungus Nomuraea rileyi is a specialized pathogen of larvae of Lepidoptera, particularly Noctuidae. In 2007 and 2014, we isolated four strains of N. rileyi (from fall armyworm, Spodoptera frugiperda, at Saltillo, Mexico) and evaluated their virulence by inoculating them topically on 3rd instar S. frugiperda larvae, in the laboratory. After wetting the larvae with the suspensions (1x10⁷ conidia/ml in water), all strains showed similar virulence causing 92-100% mortality after 6 days. Strain NR08 has been maintained in artificial media and larvae in the laboratory for seven years, and its activity was very similar (92% mortality) to that of strains kept in the laboratory for less than six months (90-98% mortality). Additional screenings are conducted to select strain(s) for field applications.