Virulence of native entomopathogenic nematodes against major lepidopteran insect species of tomato (Solanum lycopersicum L.)

In the present investigation, the bio-efficacy of indigenous entomopathogenic nematode (EPNs) Heterorhabditis bacteriophora was evaluated against the third and fourth instar larvae of major lepidopteran insect pests, viz. pod borer (Helicoverpa armigera), tabacco cutworm (Spodoptera litura), and cutworm (Agrotis segetum). Lepidopteran insect pests are responsible for causing high damage to agricultural and horticultural crops every year and it is becoming difficult to control these pests in the fields. The persistent use of chemical pesticides against these insect pests has resulted in development of resistance along with degradation of soil and human health. The two larval stages were exposed to 50, 100, 150, and 200 infective juveniles (IJs) for different time intervals and they all achieved high mortality after 120 hours. The results from the present laboratory experiment revealed that against H. armigera, the lethal concentration 50 (LC50) of third instar larvae was 60.14 IJs/larvae and fourth instar larvae was 57.90 IJs/larvae, respectively. The LC50 values of S. litura observed were 59.95 and 50.91 IJs/larvae in third and fourth instar larvae, respectively, after 120 hours of exposure. The pathogenic effect of H. bacteriophora against the third and fourth instar larvae of A. segetum showed LC50 = 54.86 and 57.90 IJs/larvae, after 120 hours. It was further evaluated that there was an increase in mortality with the advancement of larval instars. The present findings indicate that native species of EPNs show high virulence against the local insect pest of tomatoes under laboratory conditions.