Molecular Identification Of Entomopathogenic Nematodes And Evaluation Of Pathogenicities To Athetis Lepigone

More and more attention has been paid to the entomopathogenic nematodes (EPN) asan important biocontrol factor in the biological control of insect pests. Nine unknown EPNstrains, which were saved in our laboratory were classified and identified based onITS-rDNA sequence analysis. Furthermore, the symbiotic bacteria associated with theseentomopathogenic nematodes also were identified based on16S rRNA genesequence analysis. In order to evaluate the potential of some entomopathogenic nematode(EPN) species for the control of Athetis lepigone, one new pest in corn seedling stage, thepathogenicities of9EPN species of against fifth instar larvae of A. lepigone were testedunder laboratory condition. And the optimal infection condition for the EPN populationwith highest virulence was determined.1. The nine1100bp fragments of internal transcribed spacers (ITS) of rDNA wereobtained and sequenced by PCR amplification from nine EPNs. The phylogenetic analysisof the sequences of nine ITS fragments were made together with the associated sequencesof known EPN species in Genbank.16s rRNA gene sequences from the symbiotic bacteriafrom nine EPNs also were amplified by PCR method，and then compared and anlysisedwith known symbiotic bacteria of EPNs, respectively. Nine species of EPN were identifiedaccording to the EPN ITS sequences and16s rRNA gene sequences: Heterorhabditisbacteriophora HB8, H. bacteriophora HB140, H. bacteriophora XH6, Steinernemacarpocapsae NJ, S. carpocapsae HB310, S. carpocapsae GA, S. longicaudum CW105, S.longicaudum CBZB and S. glaseri NC.2. Pathogenicity of9EPN species of against fifth instar larvae of A. lepigone wereevaluated under laboratory condition. The bioassay results showed that H. bacteriophoraHB8had the strongest Pathogenicity to larvae of A. lepigone with93%the mortality after120h infection.3. Fifth instar larvae were the most susceptible stages to H. bacteriophora HB8,followed by third instar larvae, and pre-pupae or pupae the least susceptible. Furthermore,the influences of temperatures, soil moisture and EPN dosages to the pathogenicity of H.bacteriophora HB8also were tested under laboratory condition. The results showed thatpathogenicity of H. bacteriophora HB8to A. lepigone larvae was statistically significantly highest at25and30℃,15%soil moisture and50:1ratio of nematodes and insects.