Effect of the Culture Medium in the Virulence of Nomuraea Rileyi on Spodoptera Frugiperda (Lepidoptera: Noctuidae)

Isolate Nm005 of Nomuraea rileyi was selected in a previous study by causing 95% mortality in the fall armyworm Spodoptera frugiperda, the most important pest in maize crops. In order to produce high quality conidia for developing an efficient biopesticide, the objective of the present work was to determine the effect of the culture medium and some potential virulence inductors on the microbiological characteristics and biocontrol activity of the N. rileyi conidia. The fungus was grown on millet, rice, oat and soybean substrates. After evaluating yield, germination and biocontrol activity of produced conidia on the substrates, the soybean medium was selected because the conidia presented the best characteristics. In addition, the fungus was grown on yeast-malt extract agar medium supplemented with several potential inductors of virulence that consisted of two proteic inductors, a homogenization of larvae, a non specific inductor, an inductor based on a polymer and a control with no inductor. By using a bioassay, the proteic inductor 1 and polymer inductor 1 were selected because they caused an increase in biocontrol activity. Afterwards, the combined effect of the selected substrate for mass production and the selected potential inductor of virulence on the germination and biocontrol activity of the fungus was evaluated. The polymer inductor 1, combined with the culture medium, had a positive effect on the characteristics evaluated. The results obtained suggest that the type and composition of the culture medium determines the microbiological characteristics and virulence of the biomass produced.