Isolation and evaluation of Heterorhabditis bacteriophora strain-s₂₆ as biocontrol agents against Pieris brassicae L. under laboratory conditions

Entomopathogenic nematodes (EPNs) as bio-control have been reported as conventional and intensified method in insect pest management. In the present investigation, a survey was carried out in district Sirmaur to detect the presence of EPNs. In total, 110 soil samples were collected from the rhizospheric soil of fruit plantations and among them 35 samples possess EPNs. Based on morphological analysis, all the isolated EPNs were identified as Heterorhabditis bacteriophora. The insecticidal potential of local isolate of EPN H. bacteriophora strain EUPT-S₂₆ was evaluated against two different larval instars (3ʳᵈ and 4ᵗʰ instars) of Pieris brassicae (cabbage butterfly) under the laboratory conditions. Different concentrations of nematode inoculums @ 30 infective juveniles (IJs), 60 IJs, 90 IJs, 120 IJs and 150 IJs/ml along with control were applied against both the instars. The rate of pathogenicity was recorded upto 96 h. It was observed that both the instars of P. brassicae were highly susceptible for H. bacteriophora strain EUPT-S₂₆ infection. The inoculum level of 150 IJs was causing highest mortality to both 3ʳᵈ and 4ᵗʰ larval instars at 96 h of exposure. The data recorded from the present study shows lethal concentration LC₅₀=29.13 IJs (95% FL=21.92–38.71) in 3ʳᵈ instars and LC₅₀=21.62 IJs (95% FL=16.06–29.10) against 4ᵗʰ instar larvae after 96 h of nematodes exposure. It was concluded from the present investigation, that the local isolates of H. bacteriophora strain EUPT-S₂₆ showed significant mortality among both the larval instars that keeps on enhanced with the increase in nematode inoculum concentration and exposure time. Further studies are required to explore their insecticidal potential against other insect pests in the field condition also.