Cold Acclimation Of Steinernema Scarabaei And Insecticidal And Antibacterial Activities Of Their Symbiotic Bacteria

Entomopathogenic nematodes(EPN)is a pathogenic nematode carrying symbiotic bacteria and host insects.It is considered as one of the most promising biocontrol agents.In order to develop and utilize entomopathogenic nematodes and their commensal bacteria in high-cold areas and improve the freezing survival rate and storage stability of nematodes.Application of nematodes and their symbiotic bacteria in the prevention and control of local agricultural pests.This study combines indoor simulated abiotic stress conditions.The appropriate low-temperature characteristics of S.litorale isolated from Harbin city were investigated.The effects of different low temperature treatments on the freezing survival rate,storage stability,and biochemical substances: soluble sugar,glycogen,trehalose,lipid and protein content of the worms were studied.And further clarify the potential and value of development and application of S.litorale.The insecticidal activity and pathogenesis of the fermentation broth of X.bovineii(isolated from S.litorale)and X.budapestensis(isolated from S.ceratophorum)in Harbin were detected.Analysis of antibacterial activity against Fusarium nivale Ba218.The main research results obtained are as follows:(1)This study first explored the effects of different cold acclimation methods of 25?(6 d)?10?(6 d)?4?(6 d)?25?(2 d)~10?(2 d)~4?(2 d)on S.litorale in alpine regions.1)The survival rate of S.litorale after cold acclimation at-20? for 36 h was 0.9%,23.6%,20.0%,and 49.2%,respectively.Staged cooling acclimation could significantly increase the survival rate of the nematode.And no significant effect on the invasiveness of S.litorale.Appropriate cold acclimation can improve the cold resistance of S.litorale.2)After cold acclimation of S.litorale,the content of soluble sugar,lipid and trehalose in the body increased,and the content of protein and glycogen did not change significantly.The contents of protein,soluble sugar,glycogen,lipid,and trehalose in S.litorale were lower than that of direct cooling acclimation,but there was no significant difference.3)The storage stability of S.litorale after low temperature acclimation had no significant change.The survival rate was more than 65% after 7 months.The insecticidal activity of the S.litorale after cold acclimation of 10?(6 d)?4?(6 d)and 25?(2 d)~10?(2 d)~4?(2 d)at 4?for 7 months was significantly higher than that of the cold acclimation at 25?(6 d).Among them,domesticated nematodes had the highest storage capacity and insecticidal activity at 10?(6 d).(2)Insecticidal and antibacterial activity of two strains of X.bovineii and X.budapestensis fermented symbiotic strains of Harbin.1)O.furnacalis and P.xylostella were tested for insecticidal activity by feeding.The bioactivity of X.bovineii fermentation broth was the highest for P.xylostella.The corrected mortality rate was 100% after 48 h,which was significantly higher than that of X.budapestensis.The corrected mortality rates of corn borer were lower in X.bovineii and X.budapestensis strains,which were 52.18% and 55.28%,respectively.2)The corrected mortality rate of Galleria mellonell treated with X.bovineii and X.budapestensis strains reached 100% after 48 h treatment.After treatment for 1 h,blood haemolymph was observed.The hemolymphs of X.bovineii and X.budapestensis strains in the fermentation broth were light gray and dark gray respectively.The hemolymph of healthy worms was light yellow.After exposure of the hemolymph to air for 30 minutes,the healthy hemolymph became black and the hemolymph treated by the fermentation broth of X.bovineii and X.budapestensis strains remained light gray and dark gray.3)G.mellonell was injected into the fermentation broth of X.bovineii and X.budapestensis strains.There was no significant change in the hemolymph protein content and the blood glucose level dropped sharply,which was significantly lower than that of the CK control group.At 4-20 h after injection,the activation of carboxylesterase and acetylcholinesterase in G.mellonell was significantly enhanced by the fermentation liquid of both strains.The enzyme activity increased with the increase of injection time and the polyphenol oxidase showed a higher inhibitory effect.4)The fermentation broth of X.bovineii and X.budapestensis strains inhibited the growth of mycelia of Fusarium nivale Ba218.The inhibitory rate of the fermentation broth of X.bovineii strain against Fusarium nivale Ba218 was 56.92%~71.22% and the inhibitory rate of fermentation liquid of X.budapestensis strain to Fusarium nivale Ba218 was 57.01% ~ 63.73%.The bacteriostatic activity of the symbiotic broth at different temperatures had no significant effect on its antibacterial activity,and its antibacterial activity was significantly reduced after ultraviolet irradiation.The fermentation broth of X.budapestensis strain inhibited light and dark alternation in the process of Fusarium nivale Ba218,and the color of the latter mycelium changed from red to orange.The darkness of the Fusarium nivale Ba218 mycelium was changed from red to light yellow,and the mycelial growth decreased.