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Susceptibility of the Fall Armyworm, Spodoptera frugiperda, to the Fungal Pathogens Paecilomyces fumoso-roseus and Nomuraea rileyi

N. K. Maniania and J. Fargues
The Florida Entomologist
Vol. 68, No. 1 (Mar., 1985), pp. 178-183
DOI: 10.2307/3494343
Stable URL: http://www.jstor.org/stable/3494343
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Susceptibility of the Fall Armyworm, Spodoptera frugiperda, to the Fungal Pathogens Paecilomyces fumoso-roseus and Nomuraea rileyi
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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/mm2 of leaf surface and its LD 50 was 40 conidia/mm2 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/mm2 of leaf surface. This study demonstrated that P. fumoso-roseus might also have potential as microbial control agent against the fall armyworm. /// La susceptibilidad del gusano cogollero Spodoptera frugiperda hacia 6 aislados de Nomuraea rileyi (F.) Samson y 10 aislados de Paecilomyces fumoso-roseus (Wize) Brown and Smith, fueron determinados por ensallos biológicos en el laboratorio. Se encontró que existían differencias significativas en mortalidad del primer estadío y en mortalidad a través del tiempo entre las diferentes razas de los 2 hongos. Los valores calculados de LT 50 variaron entre 2 y 3.7 dias en 7 aislados de P. fumoso-roseus comparados con 5 y 10 dias en aislados de N. rileyi. Las orugas de S. frugiperda fueron muy susceptibles a 4 aislados de P. fumoso-roseus. El patotipo más activo, P. fumoso-roseus no. 32, tuvo un valor de LT 50 de 2.6 dias a una concentración de 3000 conidias/mm2 de superficie de hoja, y su LD 50 fue de 40 conidias/mm2 de superficie de hoja (mortalidad registrada a los 6 dias después de expuestas). En contraste, el mejor aislado de N. rileyi (no. 5) tuvo un valor de LD 50 de 400 conidias/mm2 de superficie de hoja. Este estudio demonstró que P. fumoso-roseus pudiese tener potencial como un agente de control microbial contra el gusano cogollero.

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