The insect-pathogenic fungus Metarhizium rileyi is highly sensitive to nutritional and environmental conditions
which makes it difficult to produce as a stable biopesticide. In this study, a Colombian isolate of this
funguswas produced in bulk, and conidia were formulated as an emulsifiable concentrate (EC). The stability of formulated conidia was studied. Conidial viability was maintained at >85 % viability for 12 m under
refrigeration and for >three months at 18 C. The pH values were stable, while contaminant content was
significantly reduced. The efficacy of the EC to control Spodoptera frugiperda (Smith)was correlated with the
storage time using different mathematical models, and conservative values of six and 12 months at 8 C and
18 C respectively, were established. Finally, the EC was evaluated in maize plants under glasshouse conditions.
The LC50 and LC90were estimated to be 1.17 104 and 4.03 106 conidia/mL respectively and a 57 %
reduction in recent damage of plants was achieved. This study demonstrated the potential of M. rileyi
formulated as EC to control S. frugiperda in maize. Therefore, it is necessary to continue developing this
biopesticide, in order to deliver a new tool to be integrated in pest management programs.