Determination Of Inseci Control Effect Of Entomopathogenic Nematode And Functional Verification Of Anti Desiccation Genes

Entomopathogenic nematode（EPN）is a biological control factor with great application potential,and has good control effects on various agricultural pests.In this experiment,the infectivity of different strains of entomopathogenic nematodes to Cylas formicarius,Spodoptera litura,and Aromia bungii was measured,and the feasibility of applying EPN under drip irrigation in the field was studied.The function of the nematode resistance gene was verified.The results of this experiment are as follows:1.Determination of control effect of entomopathogenic nematodes on different kinds of insects:Determination of the infectivity of six entomopathogenic nematodes to the late larvae and adults of Cylas formicarius（Steinernema ceratophorum HQA-87,Steinernema feltiae JY-90,Steinernema sp ZLS-3,Steinernema glaseri KG,Steinernema longicaudum X-7 and Heterorhabditis beicherriana NCWZ-1）.The results showed that six EPNs have high infectivity to Cylas formicarius.when the nematode concentration reached 500 IJs·cm^-2,the best control effect on the last instar larvae was S.glaseri KG and S.longicaudum X-7,with a mortality of100%;Cylas formicarius in adult stage are less sensitive to nematodes,S.glaseri KG and S.longicaudum X-7 has a good control effect,but the highest mortality is only 33.33%.The control effects of seven EPNs on Spodoptera litura larvae at different instars were determined.The results showed that the control effects of different isolates of nematodes on the 2^nd and 3^rd instars of Spodoptera litura larvae were better,but the effects of 4^th to 6^th instars were worse.The results showed that S.glaseri KG,when the concentration reaches 111 IJs·cm^-2,the mortality is 66.67%;S.glaseri KG and S.longicaudum X-7 had a significantly higher lethal effect on the third instar larvae at the concentration of 666 IJs·cm^-2,with a mortality rate of 96.67%and 86.66%,respectively.S.longicaudum X-7 and Steinernema carpocapsae ALL had a significantly higher lethal effect on the third instar larvae than other isolates,with a mortality rate of 77.78%and 72.33%,respectively;The mortality rate of 4^th and 5^th instar larvae is 64.11%and38.89%,respectively,due to the good control effect of S.feltiae JY-90.However,The excellent isolates of Spodoptera litura larvae in the field,S.glaseri KG,S.longicaudum X-7,S.carpocapsae ALL and S.feltiae JY-90,can be employed.Three kinds of entomopathogenic nematodes,S.ceratophorum HQA-87,S.feltiae JY-90 and H.beicheriana NCWZ-1 carried out indoor bioassay and field test on the larva of Aromia bungii.The results showed that the infectivity of S.feltiae JY-90 to the 2^nd instar larvae is the strongest,and the mortality reaches 93.33%when the concentration is 20 IJs·cm^-2;When the concentration is 50 IJs·cm^-2,the mortality rate of S.ceratophorum HQA-87,S.feltiae JY-90 and H.beicherriana NCWZ-1 to the third instar larvae reached 100%.The field test’s findings indicated the greatest mortality rate of H.beicherriana NCWZ-1 nematode to the larvae of longicorn beetle was 87.66%,and the effect was significant.2.Using drip irrigation systems to apply entomopathogenic nematodesThe effect of drip irrigation on three insect pathogenic nematodes（S.ceratophorum HQA-87,S.feltiae JY-90 and H.beicherriana NCWZ-1）in the field was tested.Using a well shaped drip irrigation belt,the pressure of the pressure pump is 0.2～0.4 MPa.The results show that nematodes can flow out with water at the main and branch pipes of the drip irrigation pipe,and there are no pests left in the drip irrigation belt.After EPN drip irrigation was applied to the field,all three insect pathogenic nematodes could survive for at least 60 days at different depths（10～60 cm）in the soil.EPN is compatible with low concentration fertilizers（potassium dihydrogen phosphate,ammonium nitrate,potassium sulfate,potassium chloride,N-P₂O₅-K₂O activating enzyme complex fertilizers）and pesticides（thiacloprid,carbendazim,imidacloprid,phoxim）.Therefore,insect pathogenic nematodes can be applied during field topdressing in production.3.Functional verification of desiccation resistance genes in entomopathogenic nematodesThe functions of nematode drying genes CL2037 and CL2161 were verified by using ds RNA in vitro immersion technology.Real-time fluorescence quantitative PCR showed that the relative expression of the CL2037 and CL2161 genes of the nematode significantly decreased after RNAi treatment.The nematodes silenced by CL2037 and CL2161 genes were subjected to high temperature,drying,and low temperature treatment,with mortality rates of 7.68%,77.17%,and 61.09%,respectively.The mortality rate of nematodes in the drying treatment group was significantly different from that in the control group.Therefore,it is preliminarily determined that both CL2037 and CL2161 genes are related to nematode desiccation resistance.