High virulence of a naturally occurring entomopathogenic fungal isolate, Metarhizium (Nomuraea) rileyi, against Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda, is a new and dangerous invasive pest in many countries. Entomopathogenic fungi (EPF) have been considered as potential biological control agents against the FAW. In this study, eight natural fungal strains were isolated from diseased larvae of FAW, and identified as Cladosporium cladosporioides (EFNL-1), Metarhizium rileyi (EFNL-2 and EFNL-8), Fusarium proliferatum (EFNL-3 and EFNL-6), F. equiseti (EFNL-4 and EFNL-5) and F. tricinctum (EFNL-7), using the morphological and molecular tools or methods. The instantaneous death risk and mortality of 3(rd)-instar larvae inoculated with EFNL-8 (1 x 10(8) conidia/ml) were significantly higher than for any other fungal isolates and for the control group. Thereafter, we tested the pathogenicity of EFNL-8 (1 x 10(7) conidia/ml) against 1(st)- to 4(th)-larvae, pupae, and eggs of FAW. The instantaneous death risk and mortality of 1(st)-instar (Median lethal time = 9.02 days; Corrected motality = 88.68%), 2(nd)-instar (12.00 days; 62.50%) and 3(rd)-instar larvae (13.79 days; 56.67%) inoculated with EFNL-8 were significantly higher than that of larvae in the control groups. When the eggs of FAW were inoculated with EFNL-8 (1 x 10(7) conidia/ml), EFNL-8 caused eggs (56.62%), and newly hatched neonates after 3 days (68.75%) and 6 days (80.60%) mortality, compared with the control groups. However, the mortality of the EFNL-8 isolate to 4(th)-instar larvae (5.00%) and pupae (14.81%) was low and did not differ from the control groups. This study identified M. rileyi EFNL-8 as a pathogenic isolate against eggs and 1(st)- to 3(rd)-instar larvae of FAW. However, further studies including field validation of this EPF biopesticide candidate should be undertaken in newly invaded areas by the pest.