Comparative efficacy of entomopathogenic nematodes, their associated bacteria and toxins against Army worm (Spodoptera Litura) on vegetables

Abstract

Entomopathogenic nematodes (EPNs) (Heterorhabditis indica, H. bacteriophora and Steinernema glaseri) were utilized against 4th instar Spodoptera litura at different concentrations (200, 300, 500, 600, and 1000). EPNs at 1000 concentration caused 100 % mortality against Spodoptera litura. Two EPNs species (S. glaseri and H. bacteriophora) were used against different Spodoptera litura larval instars. Data showed that higher mortality was recorded in 2nd larval instar. In another experiment both genera of EPNs were evaluated alone and in combination. Maximum mortality caused in combine treatment. Then bacteria isolated from different species of EPNs were utilized against 5th instar larvae of Spodoptera litura at different concentrations (4×104, 4×105, 4×106 and 4×107) for larval mortality. Mortality increased as concentration of bacterial cells increased. Two bacterial isolates at most effective concentration (4×107) selected from previous experiment were sprayed against different larval stages of Spodoptera litura. Highest mortality was recorded in 2nd larval instar followed by 5th, 3rd and 4th larval instar. Bacterial metabolites isolated from bacteria were utilized against Spodoptera litura at different concentrations (1%, 10%, 20% and 40%) in petri plate to assess larval mortality. Higher concentration (40%) caused maximum mortality against Spodoptera litura. The stored EPNs, cells and metabolites were taken, diluted and assessed for the efficacy against Spodoptera litura. Mortality was decreased as the storage time increased. Fresh suspension caused maximum mortality against Spodoptera litura. Plants were treated with EPNs, bacterial cell suspension and metabolites after 3 days of larval feeding, before larval feeding and at the same time. Results showed that EPNs, bacteria and metabolites applied at the same time with larval feeding caused maximum mortality.