Field trials on biocontrol of Spodoptera frugiperda in corn, with Nomuraea rileyi and Metarhizium brunneum, at arid and tropical locations of Mexico

The fall armyworm, Spodoptera frugiperda, is a voracious pest that causes severe damage in the vegetative and reproductive phases of corn, causing considerable losses. Entomopathogenic fungi (Nomuraea rileyi and Metarhizium brunneum) were applied in the field, starting at 50-cm tall, infested corn plants for fall armyworm biological control, in the spring and summer 2012, at two widely different locations: Saltillo, Coahuila (in the desert) and near Tampico, Tamaulipas (humid tropical). Fungi were applied at vegetative and reproductive phases of the corn plant. Fungal spores were produced on rice and applied as granular and aqueous preparations at different concentrations (10⁷-10⁸ conidia/ml or /gr). Nomuraea infection levels were highly significant (p<0.001)  in the first planting in Tampico with infection levels of 23.1 - 47.8%. No infections by M. brunneum were observed, even though Nomuraea concentrations were often lower than those of Metarhizium (because Nomuraea sporulates less abundantly). Nomuraea treatments were usually significantly different (as mycosis) from the controls at all locations. The treatment that resulted in higher mortality (54%) was Nomuraea suspension in water, 4.7 x 10⁷/ml, 5 ml/plant, at Tampico. In Saltillo the highest Nomuraea infection level was 21% of collected larvae. There was horizontal transmission of the fungus in treated plots at both locations and dates, with the fungus spreading at least 20 m away from application spots within plots. Incidence in adjacent (>80m) untreated plots was very low (0-2%). The results indicate that, after augmentation, Nomuraea is capable of establishing itself within corn plots in a growing season, in both arid (irrigated) and tropical fields. It is necessary to assess applications of Nomuraea within the first two weeks of plant emergence, when plant are the most susceptible to damage and yield reductions by S. frugiperda.