Study On Insecticidal Activity Of Xenorhabdus Nematophila HB310-59 Strain

250 strains of symbiotic bacteria were isolated from 10 strains of entomophogenic nematodes. High toxic strain was screened out through the bioassay of the 10 representative strains to 6 insects and studied on insecticidal activity. The main results of the study as follow:1 High toxic Xenorhabdus nematophila HB310-59 strain was screened and Pieris rapae with the relative sensitive insect to entomopathogenic nematode symbiotic bacteria was also screened.2 HB310-59 Strain has wide insecticidal spectrum. The corrected moralities of HB310-59 Strain to Plutella xylostella and Hencsepilachna Vigintiocyomaoata are 100% within 72hr and 120hr when it comes to Pieris rapae.The value of LC50 of HB310-59 Strain to Pieris rapae is 3.2105xl06cell/ml;the weight inhibiting rate of HB310-59 Strain to Helicoverpa armigera, Ostrinia nubilalis,Mythimna separata- Spodoptera exigua. Tenebrio molitor is 97.64%,82.34%,43.75%,91.23%,29.39% respectively within 120h.3 The study of extracellular and intracellular of HB310-59 shows that intracellular has oral toxicity and injectable toxicity and extracellar has only oral toxicity. The weight inhibiting rate that is declining according to the growth of the test insects of intracellular and extracellular dialysate to 1th instar Helicoverpa armigera are 97.8%, 93.77% respectively and 76.4%, 69.93% when it comes to 3th instar. The corrected mortalities of intracellular toxin to wax moth is 100% within 12h and the value of LD₅₀is per head 73.9ug which is the total of the protein.4 The physical and chemical speciality of HB310-59 strain.The bacterium cultivate liquid ,extracellular supernate,cell,intracellular supernate and intracellular dialysate of HB310-59 can be stored four months at least at 4癈.However,the storage of extracellular dialysate is not one and half a month only at 4癈. HB310-59 strain is stable after heating l0min at 50癈 while the insecticidal acticity will produce significant difference at 5% level when heating lOmin at 70癈. When exposed to UV light, the bacterium cultivate liquid and cell can endure 1h, 9.5h respectively and the insecticidal activity is effectless. However, when it comes to extracellular supernate,after the exposure to UV light 0.5h,the insecticidal activity will be decline significantly.Proteinase K, 1MNaCl,0.1%(w/v)SDS,50%(v/v)acetone treat dialysate of HB310-59 strain room temperature Ih, result indicate :Proteinase K do not affect dialysate oral toxicity; effect oral toxicity of 1MNaCl, 0.1%(w/v)SDS, 50%(v/v)acetone is smaller intracellular dialysate than that to extracellular. 50%(v/v) acetone affect oral toxicity of extracellular dialysatesignificantly ,0.1% (w/v) SDS affect oral toxicity of intracellular dialysate significantly.5 The insecticidal active material of HB310-59 strain is protein, stripes of SDS-PAGE electrophoresis map of intracellular toxin contain 13 stripes of extracellular, and intracellular contains other more kinds of protein than extracellular and the concentration is high also than extracellular.6 The intracellular dialysate acts on two kinds proteins when it acts on the peritrophic membrance of 5th instar Helicoverpa armigera. The time of action is from 30min to 20h of the one that the molecular weight is 76KDa or so and the time of the other that the molecular weight is 87KDa is from 8h to 48h.Futhermore,the rest of optimicroscope shows that the peritrophic membrance which was treated with intracellular toxin after 3h is stretch and ivory-white membrance also but one end is unintegrity; it will be change into fragments between 4h²8h;and after 36hr it will be stretch and ivory-white membrance; finally, it is basically the same as the CK after 48h梐n integrity.stretch and transparent membrance.