| Serratia marcescens is a gram-negative bacteria belonging to Enterobacteriaceae Serratia. S. marcescens is a type of pathogenic bacterium to incects and it can infect many kinds of their adults and larvaes. Serratia marcescens PS- 1 strain is a new pathogenic bacteria isolated from infected Phyllotreta striolata(Fabricius) larvae by South China Agricultural University research team, has significant inhibitory effect on growth and survival of Spodoptera exigua Hübner larvae and P. striolata. In order to provide a better solution for pest control, the insecticide potential of microbial pigment prodigiosin has been investigated. The study investigated the effect of crude extracted prodigiosin on growth development and population growth of S. exigua larvae and to test digestive enzymes, detoxification enzymes and protective enzymes activities. The main results are as follows: 1. Inhibition effects of crude extracted prodigiosin on the growth and development and experimental population of S. exiguaThe effects of crude extracts prodigiosin from Serratia marcescens on larvae weight gain, the developmental duration and survival rate and the population growth were investigated by adding extracts to the artificial diet feed 3rd-instar larvae of S. exigua under laboratory conditions. With the increase of concentration and treatment time, treatment group larval weight gain was significantly inhibited. After treating with the prodigiosin extracts at 0.06%, 0.15%, 0.3%, 0.6% for 1 day, the inhibition rates of weight gain were: 30.15%, 41.79%, 67.07% and 87.17% respectively, for 5 days, the inhibition rates of weight gain were: 51.75%, 83.90%, 93.48% and 96.79% respectively. The developmental duration of treated larvae was significantly longer than that of the control group. The pupal stage were not significant. Survival rates of larvae and pupae were decreased with the increase of concentration and treatment time. The fecundity is not affected significantly. These results suggested that prodigiosin extracts inhibited weight gain, the developmental duration, survival rates and population growth of S. exigua. 2. Inhibition effects of prodigiosin crude extracts on digestive enzymes of S. exiguaWith prodigiosin extract concentrations at 0.06%, 0.15%, 0.3%, 0.6% artificial diet feeding 3rd instar S. exigua larvae, insects daily digestive enzyme activity was measured after treatment. The results showed that prodigiosin extract has significant inhibition to amylase and protease of S. exigua larvae. And the inhibition enhanced with the concentration increased and enhanced. The 3rd day in treatment of 0.06%, 0.15%, 0.3% and 0.6% the average relative activity of amylase were: 94.28%, 85.25%, 65.17% and 27.77%, while the average relative activity of protease is: 83.85%, 74.53%, 50.51% and 35.01%. 3. Inhibition effects of prodigiosin crude extracts on detoxification enzymes of S. exigua.After treating with prodigiosin crude extracts the activity of esterase was activated firstly, then was inhibited. The 4th day, the treatment groups showed significantly inhibition to esterase, and with the increase of concentration the inhibition become stronger. The acid phosphatase and alkaline phosphatase were activated firstly, then were inhibited. After prolonged treatment at high concentration, the inhibition was strong. 4. Effects of prodigiosin crude extracts on protective enzymes of S. exigua.After treating with prodigiosin crude extracts the activity of superoxide dismutase(SOD) of S. exigua larvae was induced. With the the treatment time, the induction first increased and then decreased. The first day in treatment in 0.06%, 0.15%, 0.3% and 0.6%, the relative activity of SOD were: 111.15%, 107.16%, 119.94% and 140.79%. Catalase(CAT) activity is first showed increased activity, and then decreased activity. The 3rd day in treatment in 0.06%, 0.15%, 0.3% and 0.6%, the relative activity of CAT were: 88.23%, 75.94%, 63.81% and 65.49 %. 5. Inhibition effects of prodigiosin crude extracts on vitro phenoloxidase of S. exigua.A concentration of 100,250,500,1000?g / ml varies prodigiosin crude extract processing S. exigua phenoloxidase in vitro, with the increasing concentration of phenoloxidase relative activity gradually decreased. When used 1000?g / ml prodigiosin crude extracts in vitro, phenol oxidase, an enzyme relative activity fell 90.95%. The IC50 was 387.374?g/ml.In summary, prodigiosin is one of the insecticidal agent of Serratia marcescens PS-1 strain. Prodigiosin has significantly inhibition effect on digestive enzymes, detoxification enzymes and vitro phenoloxidase of S. exigua. Eventually leading to inhibition of weight gain and developmental duration and survival rate. |
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