Effects Of Nicotiana Tabacum Volatiles On The Behavior And Antennal Gene Expression Of Picromerus Lewisi

Picromerus lewisi,a member of the Hemiptera family,is a significant predatory insect that preys on various lepidopteran larvae.Recently,breakthroughs have been made in the mass rearing technique of P.lewisi,and it has been widely used in the integrated pest management of economically important crops such as tobacco.However,it has been observed in that multiple generations of artificial rearing indoors have led to a decrease in the foraging ability of P.lewisi in the wild,which has resulted in reduced pest control efficacy.Plant volatiles play a crucial role as chemical mediators in the tri-trophic interactions among plants,herbivorous insects,and their natural enemies,and understanding the chemical cues and olfactory perception mechanisms underlying the host location behavior of P.lewisi can provide a theoretical basis and technical support for the efficient utilization of this predator.Therefore,in this study,through the tri-trophic relationship among tobacco,Spodoptera litura,and P.lewisi as the research system,we isolated and identified the chemical cues involved in the host location behavior of P.lewisi,and investigated the differentially expressed genes induced by tobacco volatile compounds in P.lewisi,aiming to elucidate the mechanisms underlying the host location behavior of P.lewisi.The main results are as follows:(1)Volatile compounds emitted by tobacco plants after herbivore damage were identified.Using headspace adsorption combined with gas chromatography-mass spectrometry(GC-MS).We separated and identified the volatile compounds emitted by tobacco plants.Under the experimental conditions of this study,a total of 39 compounds belonging to different classes,including terpenes,aldehydes,alkanes,alcohols,and esters,were identified from the tobacco plants subjected to different treatments.The type or quantity of volatile compounds emitted by tobacco plants was significantly influenced by herbivore damage.Compared with undamaged tobacco plants in the control group,mechanical damage(+ water)caused the release of two new volatile compounds,β-ocimene and 3,7-dimethyl-2,6-octadien-1-yl butyrate,and the relative release amount of neophytadiene also significantly increased.In tobacco plants treated with mechanical damage(+ S.litura saliva),not only β-ocimene and 3,7-dimethyl-2,6-octadien-1-yl butyrate were produced,but also the relative release amounts of four other compounds,namely,6-methyltridecane,2-hexyl-1-octanol,3-methylpentadecane,and neophytadiene,significantly increased.After S.litura feeding,the volatile compounds emitted by tobacco plants also increased,including β-ocimene,3,7-dimethyl-2,6-octadien-1-yl butyrate,methyl salicylate,3,4-dimethylacetophenone,β-elemene,and pentadecane.(2)The behavioral effects of tobacco volatiles on the predator P.lewisi were identified.Different treatments with volatiles or characteristic compounds were tested for their attraction or avoidance effects on P.lewisi applying a Y-tube apparatus.The results showed that tobacco volatiles from the mechanical damage(+water)treatment group,mechanical damage(+S.litura saliva)treatment group,and S.litura feeding treatment group all had an attraction effect on P.lewisi,and the attraction effect of tobacco volatiles from the mechanical damage(+S.litura saliva)treatment group and S.litura feeding treatment group on P.lewisi had significant differences.The attraction or avoidance effects of tobaccospecific volatiles on P.lewisi indicated that 10-3 mol/L and 10-4 mol/L β-ocimene,10-4mol/L methyl salicylate,and 10-3 mol/L and 10-4 mol/L β-farnesene all had significant attraction effects on P.lewisi,while 10-2 mol/L butyl hexanoate,methyl salicylate,and pentadecane all had significant avoidance effects on P.lewisi.(3)Transcriptome sequencing and bioinformatics analysis of P.lewisi antennae sample that exposed to tobacco volatiles after different treatments were performed.Gene expressed of P.lewisi can be devided into 13 co-expressed gene modules via Gene co-expression network analysis(WGCNA),among which the largest co-expressed module had the highest expression level under the mechanical damage(+S.litura saliva)treatment,followed by the S.litura feeding treatment group.Regarding differentially expressed genes(DEGs),compared with the control group,the mechanical damage(+water)treatment group induced the least amount of DEGs,while the mechanical damage(+S.litura saliva)treatment group induced the most DEGs.KEGG enrichment analysis showed that the specific DEGs induced by mechanical damage(+S.litura saliva)treatment group were mainly enriched in neuro-related pathways,while the specific differentially expressed genes induced by S.litura feeding treatment group were mainly enriched in immune-related pathways.A total of 46 olfactory-related genes were identified in the P.lewisi transcriptome through homologous search,including OBPs,CSPs,IRs,ORs,and SNMPs gene families.Among them,13 olfactory genes were commonly up-regulated in both the mechanical damage(+S.litura saliva)treatment group and the herbivore-induced plant volatile(HIPV)treatment group,while 11 olfactory genes were specifically up-regulated in the P.lewsis feeding treatment group.In summary,this study found that the predator P.lewsis preferred damaged tobacco plants.Mechanical damage(+ Water),mechanical damage(+S.litura saliva),or(+S.litura feeding)caused changes in the composition and relative release of tobacco volatiles,and exposure to tobacco odor under different treatments induced differential gene expression in the antennae of P.lewsis.The gene expression patterns of P.lewsis were different between the mechanical damage(+S.litura saliva)and P.lewsis feeding treatments and the mechanical damage(+water)treatment group.The results provide a theoretical basis for further exploring the host location mechanism of P.lewsis.