Screening Of Fine Strains Of Entomopathogenic Nematodes And Analysis Of Its Biological Control

Entomopathogenic nematodes(EPN) as an important biological control of insect pests has been paid more attention. we gathered 122 soil samples from Shandong province and isolated entomopathogenic nematodes named JNR, a strain of Heterorhabditis. After amplified ITS-r DNA and D2-D3 sequence and building the phylogenetic tree, JNR has the closest genetic relationship with Heterorhabditis bacteriophora.Moreover, in order to discover the potential on biological control we also study its biological characteristics. The main results are as follows:(1) 122 soil samples were collected from 13 regions with 16.39% detection rate in Shandong Province. It was determined that occurrence of EPN was closely related to the soil types, plant species and moisture. Research showed that the nematodes detection rates in sandy loam soil, sandy soil and loam soil were 28%, 18.87% and 8.57% respectively. Results showed that the nematodes detection rates were different in different plant species with the high in orchards, low in cereal fields and non-cultivated lands.Besides, we can find more nematodes when the moisture of soil was about 15%-25%.(2) The biological characteristics of one fine quality strains JNR out of others were studied.(3) After amplified ITS-rDNA and D2-D3 sequence, 992 bp、898 bp respectively, and building the phylogenetic tree, JNR has the closest genetic relationship with Heterorhabditis bacteriophora, a strain of Heterorhabditis.(4) We studied the infectivity of entomopathogenic nematodes to Galleria mellonella under different dosages, and results showed that the correction mortality rate increased with the increase of concentration. The correction mortality was 0% under dosages of 10~60 IJs/larve for 24 h, and the hosts all died after 72 h.(5) We discussed the effects of temperature and moisture on EPNs, survival and infectivity. Nematodes JNR had fine haet tolerance,and can survive for 32 h under 38 ℃ with infectivity while all died for 3 h under 40 ℃. The nematode JNR can live for days exposed to 5℃、10℃ and the infectivity increased with the increase of temperature.(6) Research showed that JNR’s ability of transverse diffusion at 30 ℃ was better than that at 18 ℃ and 25 ℃. There was 31% individuals could move to 3.6 cm in 48 h at 30 ℃ while there was only 10% individuals at 18 ℃. JNR can make G.mellonella die for 44 h in vivo at 25 ℃, which had significant difference with S. litorale and S.ceratophorum. Moreover, H. bacteriophora JNR had shorter infection cycle at 30 ℃ than 25 ℃ and was more suitable than the other two nematodes.(7) Virulence of nematode JNR strain to white grub at different dosages in lab was determined. The study demonstrated that JNR had practical potential in controlling white grubs, especially under 500IJs/larve for 72 h, making 88% mortality, and all died for 96 h while i t will need 120 h under 200IJs/larve.