Study On Olfactory Mechanism Of Host Selection On Chilo Auricilius(Dudgeno)

Rice is an important food crop.To prevent and control rice pests and diseases is an important role in safe and high yield.Chilo auricilius(Dudgeno)larvae feeds on a wide range of food crops,including Oryza sativa,Saccharum officinarum and Zea mays.As a particularly incident minor pest of rice in some areas,C.auricilius had risen as the main pests.It was reported that C.auricilius had host selection behavior during rice heading stage.Studying the olfactory mechanism of feeding-selection can help us to further understand the relationship between the adaptation and the host plant,and provide a basis for the forecast and comprehensive control technology system.The host selection behavior of insects is a continuous process.Insects use their sensitive olfactory system to orient long-distance plants.They identify and select feeding or spawning sites after reaching plants.This article intends to start with two aspects of insect olfactory genes and host odor molecules.Firstly,Y-type olfactometer was used to compare the preference of C.auricilius on volatile matter at different stages of rice.The results showed that it had a clear preference for odor molecules at rice heading stage.Through dynamic headspace adsorption and gas-mass spectrometry techniques,the main volatiles of rice during the heading period were identified.The results showed that there were significant differences in the composition of volatiles substances in different growth stages of rice.Among them,the content of ?-pinene was significantly different in the tillering and heading stages of rice.According to reports,the olefin compounds were selected in the insect host and the process,which has played a very important role,so we speculate that ?-pinene may also play an important role in the host selection of C.auricilius.The synthesis of ?-pinene in rice is mainly regulated by the terpene synthase genes and named OsTPS.In this study,the relative expression levels of OsTPS2,OsTPS6,OsTPS7,OsTPS8,OsTPS9,OsTPS14,OsTPS16,OsTPS23,OsTPS25 and related genes in rice at the heading stage were significantly higher than those in tiller stage by RT-qPCR.This showed that OsTPS related genes may be involved in the changes of ?-pinene content in rice volatiles,and thus participate in the regulation of insect behavior.To further study the relationship between host-selective behavior and olfactory related genes in C.auricilius,the RNA-seq technique was used to analyze the transcriptome.The total number of total unigenes was 5839 with an average length of 1460 bp.It was identified and named the olfactory-related proteins in the transcriptome,and the genes of odorant receptors(OR),ionotropic receptors(IRs),odorant binding proteins(OBPs)and chemosensory proteins(CSPs)were screened and the numbers of genes is 3,16,9,and 19 respectively,which provided the relevant basis for subsequent experiments.The expression characteristics of ORs,IRs,OBPs,and CSPs genes were studied in different host plants of C.auricilius by real-time fluorescent PCR.When compared to feeding rice,the expression of genes IR4,IR5,IR11,IR12,OBP2,OBP3,OBP6,CSP5,CSP7,CSP8,CSP9,CSP10,CSP11,CSP17,and CSP19 increased,and the expression levels of genes IR9,IR14,IR15,and CSP4 decreased.It showed that there is indeed an olfactory adaptation situation for different hosts in C.auricilius.Finally,combining odor molecule studies,this study found that the relative expression levels of OR2 and OBP4 genes were significantly increased and the relative expression levels of OBP3 were significantly decreased and there was no significant difference among other genes.In summary,both ?-pinene in rice and genes OBP3,OBP4,and OR2 of C.auricilius may be involved in the identification of volatiles from host transformation in C.auricilius.It is true that the adaptation of insects and host selection is a complex biological process.This paper presents a preliminary study on the host selection mechanism of C.auricilius,which will help provide a certain reference value for its comprehensive control method technology and insect-host selection.