Metarhizium rileyi biopesticide to control Spodoptera frugiperda: stability and insecticidal activity under glasshouse conditions

The dimorphic insect-pathogenic fungus Metarhizium rileyi is highly sensitive to nutritional and environmental conditions compared with other entomopathogenic fungi, being difficult to produce and formulate as a stable product. In the present study, a Colombian isolate of this fungus was massive produced and conidia were formulated in emulsifiable concentrate product. The stability of formulated conidia stored during 12 months at 8°C and 18°C was studied evaluating microbiological, physicochemical and biological parameters. Conidia germination maintained over 80% for 12 months under refrigeration and for six months at 18°C. The pH values were stable in the range between 7.00 and 7.37, while the contaminants content significantly reduced during the 12 months of storage at both temperatures. The efficacy of formulated product was correlated with the storage time using different mathematical models and the best fit was achieved with a polynomial model, which was used to estimate the shelf life, with values of 11 and 26 months at 8°C and 18°C respectively. Finally the formulated biopesticide was evaluated spraying maize plants under glasshouse conditions. The mean (LC50) and ninety (LC90) lethal concentrations were estimated in 1.17 x 104 and 4.03 x 106 conidia/mL respectively and 57% reduction in fresh damage of plants was achieved with the application of this biopesticide. This study demonstrated the potential of this biopesticide to control S. frugiperda in maize, being necessary to continue its development a scaling up in order to deliver a new tool, able to be included in integrated manage programs for different crops where the fall army worm is an economically important pest.