Study On The Direct Defense Mode Of Different Pepper Varieties Against Spodoptera Litura

Insect resistance is an important characteristic of pepper self defense,but seldom reports were foucused on the resistance of different pepper varieties to Spodoptera litura larvae.In this study,we first evaluated the repellency of several pepper varieties to S.litura,and clarified the main volatile compounds that influenced the olfactory selection of S.litura.Followed by,the biological performance of S.litura on two pepper varieties with the greatest differences in repellency was studied.The main secondary insect-resistant substances,structural substance(flavonoids,tannins,total polyphenols and wax content),and nutrient substances(amino acids,VC,protein content,crude fiber and soluble sugar content)of these two peppers were determined and analyzed.The relationship between biological parameters of S.litura and biochemical indexes of peppers was analyzed.the research results are as follows:(1)S.litura larvae preferred to choose chao tian chilli(BLTY 2).Pepper leaves of screw pepper(QM),cayenne pepper(FXBX),sheep horn pepper(BLZX 1),wrinkled sheep horn pepper(ZPL),hot pepper(215),chao tian chilli pepper(BLTY 2),and sweet pepper(XTJW)was selected to perform the repellency detection.For the evaluation of the repellency of S.litura,the third instar larvae can find their preferred leaves of the host plant in the petri dish through comprehensive factors and judge its suitability.No matter the selection experiment of seven or four varieties,the selection rate of S.litura to cayenne pepper(FXBX)was significantly lower than that of chao tian chilli(BLTY 2).(2)Qualitative and quantitative analysis of the volatile components in cayenne pepper(FXBX)and chao tian chilli(BLTY 2).The number of green leaf volatiles(GLVs)produced by the leaves of the chao tian chilli(BLTY 2)is significantly lower than that of the cayenne pepper(FXBX)leaves.The volatile content of esters and phenols in cayenne pepper(FXBX)is significantly lower than that in chao tian chilli(BLTY 2).Volatiles 1-hexene,n-hexanal,nonanal,(E)-2-hexenal and β-ionone in cayenne pepper(FXBX)are significantly higher than those in chao tian chilli pepper(BLTY 2).The volatile components of methyl salicylate and(E,E)-2,4-heptadiene aldehyde in chao tian chilli pepper(BLTY 2)are significantly higher than those in cayenne pepper(FXBX).Among alkanes-volatiles,pentane,eicosane and isohexane were only detected in the cayenne pepper(FXBX)leaves,tetradecane,pentadecane,hexadecane and heptadecane were only detected in chao tian chilli(BLTY 2),while hexanoic acid leaf alcohol ester was only detected in the cayenne pepper(FXBX)leaves,and(E,E)-2,6-nonadialdehyde and limonene were only detected in the chao tian chilli(BLTY 2)(3)The pepper volatiles that can influence selection behavior of S.litura larvae was identified.Volatile substances that affect the behavioral selection of S.litura were found to be determined by 1-hexene,hexanal,β-ionone,(E,E)-2,6-nonanedialdehyde,methyl salicylate ester,among which the substances that have the effects of avoiding S.litura under the natural release concentration of pepper are: 1-hexene,hexanal,β-ionone.(4)The effects of cayenne pepper(FXBX)and chao tian chilli(BLTY 2)varieties on the growth and development of S.litura were clarified.The Chao tian chilli(BLTY 2),which has an attractive effect on S.litura larvae,are not suitable for its growth and development,and has a repellent effect on the tested larvae.The cayenne pepper(FXBX),which has a protective effect to the tested larvae,has the same effects as artificial feeding and is suitable for its growth.(5)The relationship between the biochemical indexes of pepper leaves and the growth and development of S.litura larvae was estimated.The relationship between the biological parameters of S.litura and the main nutrients,structural substances and secondary metabolites in pepper leaves was studied by redundancy analysis method.Larvae survival rate,larval survival rate,emergence rate,female adult life span,pupal weight and emergence rate of S.litura were positively correlated to nutrients VC,amino acids,protein,cellulose and soluble sugar,and negatively correlated with wax and flavonoids.