Evaluation Of Pathogenicity And Biocontrol Effect Of Cordyceps Javanica Bd01 On Spodoptera Litura

Spodoptera litura is one of the important agricultural and forestry pests.Due to the long-term non-selective use of chemical pesticides,the resistance of S.litura is gradually enhanced.Therefore,it is imperative to develop new pollution-free control methods.Biological control is currently considered to be the most promising method.Using biological control instead of chemical control is an important goal for future development.The use of entomopathogenic fungi to control agricultural pests has become a research hotspot.In this experiment,the pathogenicity of Cordyceps javanica Bd01 was detected by S.litura.Firstly,the toxicity of different concentrations of C.javanica Bd01 to the 3rd instar larvae of S.litura was determined,and the culture conditions of C.javanica Bd01 were optimized.Secondly,the effect of the strain on the growth and development of S.litura was explored,and the changes of protective enzymes,detoxification enzymes and protein content of S.litura at different times after infection were determined.Finally,the field control effect of the spore suspension of the strain was evaluated.It provides an experimental basis for the future application of the strain for biological control.The results of this study are as follows:1.The effects of C.javanica Bd01 on the virulence and growth of the 3rd instar larvae of S.lituraThe cumulative mortality of the 3rd instar larvae of S.litura increased with the increase of spore suspension concentration.When the spore suspension concentration was 1.0×10⁸spores/m L,the corrected mortality reached a maximum of 88.68%,LT₅₀was 3.11 d,and LC₅₀was 4.68×10⁵spores/m L.The higher the concentration of Bd01spore solution,the longer the developmental duration of larvae.The developmental duration of larvae treated with 1×10⁸spores/m L was 3.00 days longer than that of the control.The developmental duration of the prepupal and pupal treatment groups was slightly shorter than that of the control.The cumulative mortality of S.litura in the whole growth and development stage showed a gradually increasing trend with the increase of spore concentration.When S.litura successfully emerged to the adult stage,the cumulative mortality of S.litura treated with 1×10⁸spores/m L spore solution was the highest,reaching 70%,the pupation rate was 43.33%,the emergence rate was 30%,and the number of eggs laid was 421.33.Compared with the control,the number of eggs laid decreased by 1214.34.The pupal weight of S.litura treated with different concentrations of spore suspension increased compared with the control.The higher the concentration,the lower the hatching rate of eggs,the lowest was 39.67%.2.Optimization of culture conditions of C.javanica Bd01 by response surface methodologyWhen the nutrient content of the medium was 30 g/L,the carbon source was glucose,the p H was 7.5,and the illumination time was 12 h,the strain grew best.The optimal sporulation conditions of C.javanica were obtained by response surface methodology.The optimal sporulation conditions of C.javanica were as follows:the nutrient content of the medium was 30.24 g/L,the p H value was 7.55,and the illumination time was 12.06 h.Under these conditions,the sporulation of the medium was 2.78×10⁸spores/m L.The actual measurement results are basically consistent with the model prediction results,which can be used for mass production of spores.3.The effects of Bd01 on the activities of protective enzymes and detoxification enzymes in S.litura larvaeAfter S.litura was infected by Bd01,the catalase（CAT）activity reached the maximum at 48 h,and the overall trend increased first and then decreased.The activity of peroxidase（POD）increased first,then decreased,then increased,and finally decreased,reaching the maximum at 48 h.The activity of superoxide dismutase（SOD）increased first and then decreased,and reached the maximum after36 h of treatment.The activity of SOD in S.litura was higher than that in the control group during the whole treatment period.Glutathione-S-transferase（GST）reached the maximum after 48 h of treatment,carboxylesterase（Car E）reached the maximum after60 h of treatment,and protein content reached the maximum after 36 h of treatment.4.Application and verificationThe control effect of 1×10⁸spores/m L spore solution on S.litura reached a maximum of 71.67%under indoor conditions and 56.67%under natural conditions.It is an effective method to control the agricultural pest S.litura by using C.javanica.