Laboratory and Field Performance of <i>Metarhizium anisopliae</i> Isolate ICIPE 41 for Sustainable Control of the Invasive Fall Armyworm <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae)

To overcome the negative impacts of invasive fall armyworm (FAW), this study assessed the laboratory and field efficacy of aqueous and oil-based formulations of <i>Metarhizium anisopliae</i> ICIPE 41 as an alternative source for FAW management. Three oil formulations, including canola, corn and olive oils and an aqueous formulation of ICIPE 41, were assessed against the second-instar larvae of FAW in the laboratory. Field experiments were also conducted at Mbita and Migori, Kenya, using the formulation that performed best in the lab, with four treatments: (a) A corn oil formulation of ICIPE 41; (b) Mazao Achieve^® biopesticide, with the <i>M. anisopliae</i> ICIPE 78 strain as the active ingredient; (c) spinetoram-based synthetic pesticide; (d) a control (water + corn oil). FAW incidence, infestation, larval mortality and the effects on parasitoids and yield were evaluated. The laboratory results showed no significant differences in the efficacies among the oil-based formulations, with mortality rates of >70% and an LT₅₀ of ~2 days compared to 15.15% in the controls with an LT₅₀ of 8.11days. Under the field conditions, no significant differences in the FAW infestation were observed between ICIPE 41 and Mazao Achieve^®, compared to the control treatments in both agro-ecological zones. From the field-collected samples, both fugal-based biopesticides exhibited high mortality and mycosis rates, with no negative impacts on <i>Cotesia icipe</i> compared to the spinetoram pesticide. There were significant differences in the total grain yields among the treatments in Mbita and Migori. Therefore, ICIPE 41 formulated with corn oil could be used for sustainable FAW management in maize cropping systems.