Studies On The Pathogenicity Of Entomogenous Nematode And The Insecticidal And Antimivtobial Activity Of Photorhabdus Luminescens

In this paper, Entomogenous nematodcs. Helerorhabditis bacteriophora from Canada were tested for its pathogenicity to four species of insects. Studies were conducted to evaluate the interaction of nemalode-bacterium-insect and the ability of Photorhabdus luminescens to produce antibiotic compounds on an artificial medium and in the nematode-parasitized host, Galleria mellonella and the characterization of antibacterialtoxin.Laboratory evaluation of pathogenicity of entomogenous nematodes. H.bacleriophor io P.rapae, G. mellonella, H.armigenui. M. alternatus were conducted. The results indicated that a broad-spectrum of insects were infected by entomopathenic nematode. Maximum mortality of 90-100% of the larvae of Pieris rapae: G.mcllonclta. H. armigema was noticed within 48h from the start of the experiment. H.bacteriophor can resulled in death of the adult of M. alternatus within 3-7days. a comparatively high concentration was needed to obtain high mortality in all insects. Studies have been carried out on the effect of temperature on the infectivity of H bacteriophora to adults of Monochamus alternatus. H. bacteriophora showed a much higher infective efficacy from 20 Cto 30 C. Once temperature was below 20 C or beyond 30 C, the infectvie efficacy of nematode declined to 20%.P.luminescens, a bacterium symbiotically associated with the insect-parasitic nematode H.bacteriophora, exists in two morphologically distinguishable phases (primary and secondary), when cultured in vitro. Only I phase was found in nematode and responsible for the death of the insect host. Ten cells can lead to the death of insect. G.mellonella larvae infected with nematode soon showed (24h) the typical growth of its symbiotic bacterium and, in parallel, the growth of another Grem negative bacterial species in the body cavity. The population of symbiotic bacterium increased rapidly to 4 106 cell g-1 wet G.mellonella larvae within 24h and maintained a relatively constant lcvel(4.8-5.8 109) through the entire 10-days period of nematode development. A population of Entercoccus sp in the nematode infected larvae collapsed to zero by 96h.Metabolites produced by P.luminescens in vivo and vitro was assayed on petri plates of B.subfilis to test for antibacterial activity and of B. cinerea to test for antimycotic activity, and of injecting G.mellonella to test insecticidal activity. The results showed that the level of antibacterium followed a pattern similar to that of the growth curve to stationary phase of the P.luminescen. The antimycotic activity was not found over a period of 240h. When symbiotic bacterium was cultured at 150rpm. 25 C, in vitro NB for 72h, it had a stronginhibiting activity against B. subtilis but not nnlimycotic activity and was found highly toxic to G.mellonella. At 48h, the longest radius of inhition zone was 5.5 mm. Total complex were precipitated with ammonium sulfate 80% saturation from cell-free culture .The crude extract couldn't tolerate high temperature. t 40 C, antibacterial activity was lost. The crude extracts were purified through a series steps including dialysis and gel filtration chromatography with Sephadex G-100 column. The peak V was active against B.subtilis. All the peaks had no toxity when injected G.mellonella.In order to promote active substance production, fermentation condition of symbiotic bacterium was optimized. Results were that the culture filtrates in NB showed the strongest insecticidal activity against G.mellonella at 25 C, 30 C. Rotation speed had no effect on insecticidal activity. The antibacterial activity to B.'suhtilis was the strongest at A2B2,A3B2. the longest radius of inhition zone is 6.5 mm.