Study On Insecticidal Activity Of Symbiotic Bacteria From Entomopathogenic Nematodes

Xenorhabdus and Photorhabdus are entomopathogenic bacteria symbiotically associated with insect pathogenic nematodes. They are highly virulent to insects. Bowen reported that Photorhabdus luminescens W-14 could produce a protein complex that was lethal when given orally or injected. This discovery arouses general concern .124 strains of symbiotic bacteria were isolated from 4 strains of entomopathogenic nematodes. Bioassays showed the insecticidal activities vary according species and isolates. The highly virulent strains is selected through a large number of bioassays.Xenorhabdus sp.HB310 has oral insecticidal activity. This bacteria has the features as follow:1. X. sp.HB310 has highly virulent to Plutella xylostella, Helicoverpa annigera^ Pieris rapae- Galleria mellonella, Mythimna separata^ Ostrinia nubilalis ^ Tenebrio molitor larvae. The insecticidal toxins is extracted primarily. The insecticidal toxin inhibited the growth of H. armigera. The average inhibiting rate of larval weight can reach 96.04%.2. X. sp.HB310 is substantially heat stable to 50.3. X. sp.HB310 is also stable to Ih sunlight 60min unltraviolet ray. SoX. sp.HB310 is potential as biocontrol agent.Phase variation was a feature to entomopathogenic nematodes bacterium. The insecticidal activities of phase I and II of HB310 were studied. The research showed I phase was highly oral and haemocoel insecticidal activity to insects; but II phase was low.The taxonomy of nematode species HB310 is defined by cross-breeding experiment The result showed HB310 has highly relative with S. carpocapsae.