Isolation,Identification,and Insecticidal Activity Of Purpureocillium Lilacinum PL-1 Against Myzus Persicae And Spodoptera Frugiperda

Green peach aphid（Myzus persicae）is a common polyphagous insect of Hemiptera.It has a wide range of hosts.It can absorb plant SAP,secrete honeydew,cause Sooty Blotch,and transmit various plant viruses.Fall armyworm（Spodoptera frugiperda）is a lepidoptera moth pest that has invaded China in recent years.It mainly damages Gramineae crops,such as corn and wheat,with strong reproductive ability,migratory ability and drug resistance.Purpureocillium lilacinum is an eco-friendly biocontrol fungus that has been widely used in the biological control of root-knot nematodes.However,its insecticidal activity against agricultural pests has not been widely studied.In this study,a strain of P.lilacinum was isolated from soil,and its morphology and molecular identification were carried out.The growth rate,sporulation quantity,protease and chitinase activities were measured and compared with Beauveria bassiana ARSEF 2860.The virulence of aphid persicae and S.frugiperda were studied by spore impregnation method and injection method respectively.The LC₅₀and LT₅₀of M.persicae and S.frugiperda larvae were determined.The parasitism effect of conidia impregnation on eggs of S.frugiperda was studied.The expression levels of related immunity and virulence genes in larvae of S.frugiperda were analyzed by real-time quantitative PCR.In this study,the biological control potential of P.lilacinum PL-1 against two representative agricultural pests was investigated,which provided a new idea for pest control.The main results are as follows:1.Isolation and identification of P.lilacinum:The fungal strain was isolated from the soil on the campus of Anhui Agricultural University in Hefei,and identified as P.lilacinum through ITS sequencing and morphological identification,named PL-1.The conidia,spore and sporulation structure were observed by light microscope and electron microscope.2.Determination of growth rate,sporulation and enzyme activity:The growth rate of PL-1 on the last 6 days was faster than that on the first 6 days,and sporulation on the 12th day was higher than that on B.bassiana ARSEF 2860.The chitinase activity of PL-1 increased from day 3 to day 6 and reached the highest value.The activity of protease began to increase rapidly on day 6 and reached the maximum value on day 9.3.Determination of insecticidal activity against M.persicae and S.frugiperda:The toxicity of PL-1 to M.persicae showed that the cumulative mortality rate of M.persicae increased gradually with the increase of time,and the LC₅₀at 96 h was2.3×10⁸conidia/m L.After 168 h,the cumulative mortality of M.persicae inoculated with different concentrations of PL-1 reached the highest value,and the cumulative mortality of 10⁹conidia/m L reached 100%.The concentration of inoculated conidia increased from 10⁷to 10⁹conidia/m L,and LT₅₀decreased from 116.51 h to 83.30 h.The results of virulence test showed that although the larvae of S.frugiperda could not be killed by impregnation method,the cumulative mortality of S.frugiperda larvae reached 88%and 97%after injection of 2×10⁵and 1×10⁶conidia for 108 h,respectively.The LT₅₀of 2×10⁵conidia was 86.64 h,and that of 1×10⁶conidia was68.42 h.LT₅₀of 2×10⁵conidia inoculated was 86.64 h,and LT₅₀of 1×10⁶conidia inoculated was 68.42 h.After impregnation,the eggs were colonized by PL-1 after 60h.4.Expression analysis of differentially expressed genes related to infection process:q PCR was used to analyze the expression changes of genes related to insect immunity and fungal virulence during PL-1 infection of S.frugiperda.larvae.The results showed that the genes encoding antimicrobial peptide,C-type lectin,lysozyme,phenoloxidase and peptidoglycan recognition protein were significantly changed.Fungal virulence genes that expressed significant changes included genes encoding chitinase,protease,lipase and hydrophobic protein.