Dusting Metarhizium rileyi conidia with a drone for controlling fall armyworm and soybean looper in maize and soybean fields

Exploring the utilization of drones for field applications of entomopathogenic fungus as a dry powder marks a pioneering effort in pest management. In this study, Metarhizium rileyi isolates CG381 and CG1153 were utilized to target third instar larvae of Spodoptera frugiperda in maize and Chrysodeixis includens in soybean field plots, respectively. A drone, calibrated to dispense the equivalent of 50 g of non-formulated conidia per hectare (approximately 5 × 10 12 con ha −1 ), was utilized, with untreated plots and plots treated with an equivalent dose using a CO 2 -powered backpack sprayer serving as controls. The application of M. rileyi via spraying exhibited uniformity with minimal drift, with 88% of the expected conidia per unit area collected by conidial collectors. However, the recovery rates after dusting on soybean and maize plants were estimated to be only 3.4 and 16.2%, respectively, with less uniform distribution. Despite this, infection rates in dusted plots were comparable to those achieved with conventional spraying, ranging from 35–48% for S. frugiperda to 29–34% for C. includens . Laboratory susceptibility assays revealed higher infection levels when first instar larvae were fed M. rileyi -dusted leaves, emphasizing the importance of accurate pest monitoring for optimal timing of drone applications or other methods. While adjustments are necessary to improve both conidia deposition and operational efficiency, our findings demonstrate the significant potential of drone-based conidial powder release for caterpillar management in soybean and maize fields.