Susceptibility of the Fall Armyworm, Spodoptera Frugiperda, to the Fungal Pathogens Paecilomyces Fumoso-Roseus and Nomuraea Rileyi

Abstract

Laboratory bioassays determined the susceptibility of the fall armyworm Spodoptera frugiperda Smith to 6 isolates of Nomuraea rileyi (F.) Samson and to 10 isolates of Paecilomyces fumoso-roseus (Wize) Brown and Smith. Significant differences in first-instar mortality and in time-mortality response were found to exist between the different strains of the 2 fungi. Calculated LT 50 values varied between 2 and 3.7 days for 7 P. fumoso-roseus isolates as compared to 5 and 10 days for the N. rileyi isolates. S. frugiperda caterpillars were highly susceptible to 4 strains of P. fumoso-roseus. The most active pathotype, P. fumoso-roseus n@* 32 had a LT 50 value of 2.6 days at the concentration of 3000 conidia/mm^2 of leaf surface and its LD 50 was 40 conidia/mm^2 of leaf surface (mortality recorded at 6 days post-exposure). In contrast, the best N. rileyi isolate (n@* 5) had a LD 50 value of 400 conidia/mm^2 of leaf surface. This study demonstrated that P. fumoso-roseus might also have potential as microbial control agent against the fall armyworm.