Effect Of Gut Microbiota On The Bt Susceptibility In Diamondback Moth,Plutella Xylostella(l.)

The diamondback moth is a worldwide pest with strong insecticide resistance.It is not only resistant to a variety of chemical insecticides,but also the first insect to report resistance to Bt in the field.It's high resistance brings great pressure to the control of Plutella xylostella.Recent studies have shown that gut microbiota are involved in host Bt resistance.Our previous study has found that the gut microbiota of P.xylostella are closely related to the growth and development of the host,but the relationship between the gut microbiota and the Bt resistance of the host is still unclear.On the basis of previous work,this study further analyzed the effect of gut microbiota mediated Bt resistance of P.xylostella,so as to provide a new perspective and thinking for biological control of P.xylostella.The main results are as follows:1.Gut bacteria mediated changes in the sensitivity of the P.xylostella to Bt.In the experiment,it was found that recovery of all the gut bacteria(The mixed bacteria isolated from the gut contents of the conventional rearing P.xylostella were cultured and enriched in LB medium)to the sterile third instar larval was able to reduce the insecticidal activity of Bt8010,and the results of single strain recovery showed that different gut bacteria had different effects on the Bt sensitivity of the P.xylostella.Serratia marcescens-IAE6(Sm PXG6)and Bt8010 strain combination increased the insecticidal rate of Bt8010,the Sm PXG6 has a synergistic effect with Bt8010,however,the Enterobacter sp.IAE5(Eb PXG5)lowered the sensitivity of P.xylostella to Bt8010,and the effects was enhanced when the concentration of Eb PXG5 was increased.Further study found that the Eb PXG5 mediated the change of P.xylostella Bt sensitivity,which was not related to the extracellular secretion and bacterial content of the strain.2.In vitro bacteriostatic test showed that Eb PXG5 had no inhibitory effect on Bt8010,but there maybe niche competition between Eb PXG5 and Bt8010 in the gut environment.Plate culture analysis showed that strain Bt8010 could be detected in the gut of the P.xylostella fed with strain Bt8010 for 24 h,while no Bt8010 was detected in the gut of the P.xylostella fed with strains Eb PXG5 + Bt8010.After feeding for 36 h,the number of cultured strain Bt8010 in the gut of P.xylostella larvae which fed with Eb PXG5 + Bt8010 strain was far less than that of the treatment group fed with Bt8010 strain alone.After feeding for 48 h,a large number of Bt8010 was detected in the hemolymph of the P.xylostella treated with Bt8010,but no Bt8010 was detected in the hemolymph of the P.xylostella treated with strains Eb PXG5 + Bt8010.The above results suggested that the gut bacteria Eb PXG5 reduced the colonization of Bt8010 in the gut,weakened the damage of Bt8010 to the gut epithelium and its invasion to the hemolymph of the P.xylostella,which played an important role in protecting the P.xylostella and reducing the Bt sensitivity.3.In order to further analyze the protective effect of Eb PXG5 on the gut of the P.xylostella,Scanning Electron Microscope(SEM)was used to study the differences in the effects of different bacterial treatments on the gut epithelium.Our results showed that a large number of Eb PXG5 colonization was found in the P.xylostella midgut when feeding with Eb PXG5,the gut epithelium was more healthy.However,the midgut of the P.xylostella which feeding with Bt8010 formed a lot of bubbles,and the bubbles were brokened to form holes,the Bt8010 gathered around the holes.Interestingly,the P.xylostella fed with Eb PXG5 + Bt8010 did not detected any bubbles as well as the corresponding holes,shows that the existence of Eb PXG5 weaked the damage caused by Bt8010.