Survival and Virulence of Native Strains of <i>Steinernema carpocapsae</i> and <i>Heterorhabditis bacteriophora</i> in Formulations

Abstract

In this study, entomopathogenic nematodes (EPN) isolated from cotton ecosystem viz., Steinernema carpocapsae (strain APKS2) and Heterorhabditis bacteriophora (strain KKMH1) were evaluated in formulations of alginate gel, talc, sponge and water concentrates. The survival or longevity of infective juveniles (IJs) in these formulations was evaluated under in vitro at storage temperatures of 5 and 25 °C. Simultaneously the virulence of these stored EPN infective juveniles (IJs) was evaluated against the spotted boll worm Earias vitella through in vitro bioassays. The results revealed that S. carpocapsae (APKS2) and H. bacteriophora (KKMH1) formulated in alginate gel survived 70-100% up to 3 months with 55-100% infectivity at 5°C and survived 52-100% with 42.5-100% virulence for 2.5 months at 25°C. In talc formulation, these EPN remained alive to an extent of 55-100% with 70-100% virulence at 5°C and stayed alive 45-100% with 52.5-100% virulence at 25°C for 2 months. In sponge formulation, EPN strains survived 55-100% with 67.5-100% infectivity for 7 weeks at 5°C, but with 50-100% survivals and 62.5-100% virulence at 25°C. EPN strain S. carpocapsae (APKS2) can be stored in water at 5°C up to 8 weeks with viability of 50% and infectivity 60%. At 25°C, it can be stored for 5 weeks with survival of 62% and infectivity of 62.5-100 %. It is inferred from the results that alginate and talc formulations at storage temperature of 5°C is better for long term storage of S. carpocapsae strain APKS2 and H. bacteriophora strain KKMH1. Thus, the results revealed that S. carpocapsae (strain APKS2) and H. bacteriophora (strain KKMH1) can be formulated in sponges for use within 2 months and can be kept as water concentrate if they would be utilized in 2-3 weeks.