Laboratory evaluation of the pathogenicity of three entomopathogenic nematodes against larvae of cabbage butterfly, Pieris brassicae Linnaeus (Lepidoptera: Pieridae)

The development of indigenously isolated entomopathogenic nematodes as biological control agents was investigated. The study involved three nematode species (Heterorhabditis indica, Steinernema thermophilum and S. glaseri) and their pathogenicity against larvae of cabbage butterfly, Pieris brassicae, under laboratory conditions. Nematodes of different concentrations (0, 10, 25, 50, 75, and 100 IJs/larva in 0.5 ml of distilled water) were applied against the insect pest using Petri dish assay. Progeny production of IJs was determined by the number of IJs produced per larva/pupa (within 20 days), following their exposure to IJs of EPN species at different concentrations. The data were analyzed statistically and the significance of the difference was determined by one way analysis of variance (ANOVA) and student’s t-test. LC 50 and LT 50 values were determined and estimated. Among the three species S. thermophilum caused larval mortality at 24 HAI (hours after inoculation) at 50 IJs/larva. However, at 48 HAI in addition to S. thermophilum, H. indica also revealed 100% mortality at 100 IJs/larva. In case of S. glaseri no mortality was observed at 24 HAI. The study thus concluded that both on the basis of mortality and LC 50 value (30.2 IJs/larva at 48 HAI) S. thermophilum emerged as the most potent species. The progeny production by larvae of P. brassicae was noted to be highest only in case of H. indica. The production increased along the concentrations till the highest concentration for both H. indica and S. thermophilum but declined from 50 IJs/larva onwards in case of S. glaseri.