Identification Of Beacteria In Gut And Screening Of Pathogens In The Cnaphalocrocis Medinalis

The rice leaf folder,Cnaphalocrocis medinalis(Guenee),is a common seasonal,migrant pest.The larvae of C.medinalis primarily feed on rice,maize,wheat,and other Gramineae crops,which causing significant economic losses in China.Currently,chemical pesticides are extensively used to control C.medinalis.However,the overuse of chemical pesticides resulted in environmental pollution,resistance,pesticide residues,and other problems.Thus,it is crucial to look towards safer,less harmful,and more effective control measures.Compared with conventional chemical pesticides,microbial pesticides have the benefits of high efficiency,selectivity,less resistance,and low toxicity.The microbial pesticides which were used for controlling C.medinalis were still limited.Hence,there is an urgent need for developing novel microbial pesticides.In present study,we isolated and identified the gut beacteria in the C.medinalis.And than we selected a highly lethal pathogen,Serratia maecescens,to identify a bacteria that have pathogenic effects on the C.medinalis.This study provided the foundation for developing microbial pesticides to control C.medinalis.The main results are as follows:1.The isolation and identification of gut beacteria in the C.medinalis and the screening of pathogenSixteen bacterial species were isolated from the gut of the wild C.medinalis using traditional culture methods.These 16 bacterias were identified as Enterobacter asburiae,Acinetobacter soli,Klebsiella aerogenes,Enterobacter ludwigii,Herbaspirillum huttiens,Pseudomonas mosselii,Enterococcus hirae,Pantoea ananatis,Klebsiella pneumonia,Bacillus atrophaeus,Chryseobacterium culicis,Stenotrophomonas pavanii,Providencia vermicola,Myroides odoratus,Pantoea dispersa and Serratia marcescens by using 16s rRNA sequencing.A high mortality beacteria strain of Serratia marcescens HY was screened by feeding different beacterias to the C.medinalis larvae,using the leaf dipping method.When the concentration of HY is 1.14×109 cfu/mL,the mortality of C.medinalis larvae reached by 79.83%.The S.marcescens HY may serve as potential biocontrol agent against C.medinalis,which could be used as an original strain for the development of microbial pesticides.2.The pathogenicity of Serratia marcescens HY to the C.medinalis larvaeThe pathogenicity of HY to the C.medinalis larvae was investigated from 3 aspects:different concentration gradients,different instar larval in high concentrations and different components.The 1.14×103 cfu/mL,1.14×105 cfu/mL,1.14×107 cfu/mL,1.14×109 cfu/mL and 1.14×1010 cfu/mL of HY caused 21.93%,30.04%,52.47%,82.15%and 98.34%mortality of C.medinalis larvaes,respectively.It caused 82.95%and 71.91%mortality of 1st and 4th instar larvae of the C.medinalis when they were treated with 1.14×109 cfu/mL HY.The cumulative mortality of 1st and 4th instar larvae treated with 1.14×1010 cfu/mL HY was 97.78%and 88.89%,respectively.The bacterial solution,suspension and supernatant of HY showed lethal effects on the C.medinalis larvaes,and the mortality was 73.81%,46.78%and 33.99%,respectively.Total of 198 proteins in the bacterial culture supernatant of HY were identified using Label-free proteomics.According to the qualitative results and related literature,we inferred that serralysin and hemolysin might be the insecticidal substances of this pathogenic bacterium.