Virulence of Philippine Entomopathogenic Nematode against Fall Armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) Strains

Abstract

Abstract The control of fall armyworm (FAW), Spodoptera frugiperda, has been a significant concern to the corn and rice in the Philippines. Recent research has focused on developing control strategies using biological controls such as entomopathogenic nematodes. This paper evaluated the efficacy of the Philippine isolates Heterorhabditis indica (HiBSDS, HiMAP, HiPBCB) and Steinernema abbasi (SaMBLB) against two strains of S. frugiperda (J.E. Smith). The Philippine EPN isolates were shown to be pathogenic to S. frugiperda regardless of FAW strains. Among the three isolates under the genus Heterorhabditids, HiPBCB was the most virulent among the test isolates tested against two strains of FAW. The result showed a high significance on the pathogenicity test exposed to all isolates at 24 hpi. The highest LC50 was observed for SaMBLB, corresponding to 36.95 IJs/larva (CS) and 35.92 IJs/larva (RS). This was sufficient to achieve 100% mortality after 48 hrs significantly differed from the three H. indica. On the lethal time (LT50) estimates, infection with H. indica in both strains had no significant differences due to the overlapping fiducial limits. However, both strains had significantly longer lethal times (LT50) when infected with S. abbasi (MBLB). No intraspecific variability was observed in the virulence of the different H. indica isolates. More apparent is the interspecific variability between S. abbasi and H. indica, as the latter exhibited higher virulence activity. This study revealed no pathogenicity variations in strains of S. frugiperda. However, it showed a different level of virulence, LC50, and LT50 between H. indica and S. abbasi.