Host Selection Mechanismof Sitodiplosis Mosellana (Gehin) (Diptera:Cecidomyiidae) Based On The Wheat Spike Volatiles

The orange wheat blossom midge,Sitodiplosis mosellana(Gehin),is a devastating wheat pest in China.The lack of resistant varieties is one of the most important reasons for the serious damage of this pest.Study on resistance mechanism crop to insect pest is a basic work in breeding insect-resistant varieties.Extensive studies have validated that the host plant volatiles play an important role in host selection of insects.In this study,wheat varieties with different resistance level to S.mosellana which had been evaluated in our lab will be used to investigate oviposition preference of the pest.Meanwhile we analyse the relationship between host plant selection and ear of wheat volatiles by dynamic headspace extraction(DHS),Gas Chromatography-Mass Spectrometer(GC-MS),Y-tube olfactometer and Electroantennogram(EAG).The results will enable a comprehensive understanding of the mechanisms of wheat resistant to the midge and have significant meanings of studying new ways of surveillance and control.The main results are as follows:1.There are significant differences of oviposition site selection of orange wheat midge to different wheat varieties.The oviposition preference of S.mosellana to different wheat hosts from high to low was Xinong 822,Xiaoyan 22,Xinong 88,Fengchan 0818,Wunong 986,Xiaoyan 6,Kenong 1006 and Zhongzhi 9;the number of oviposition in Shanmai 139 and Jinmai 47 were the least,obviously lower than the others(P<0.05).2.The ear of wheat volatiles were collected using SPME and DHS separately.After that,GC-MS determined that volatile components obtained were similar,either by SPME or DHS.Terpene and ketone compounds were the main composition,by contrast,terpene compounds acquired by SPME were more.In two wheat varieties,high content of esters were collected by DHS,but no esters could be detected by SPME.3.Two-choice bioassays of different wheat volatiles indicated that three susceptible wheat varieties(Xinong822,Xinong88 and Xiaoyan22)and one insect-resistant variety(Kenong1006)had significant attraction to adult midge,but Jinmai47 and Shanmai139(resistant wheat varieties)did not.Compared to Jinmai47 and Shanmai139,adult evidently oriented to three insect-suceptiblevarienties,while the preference of midge between Kenong1006 and three susceptible varieties differentiated a little.4.Based on two-choice bioassays,we identified 24 wheat volatiles,among whichterpenoids had 7 substances at most,in 6 different wheat varieties by GC-MS.The same matters of all varieties were 3-hexanol,cis-3-hexenyl acetate,ocimene,?-cedrene,caryophyllene,dodecane and tridecane,respectively.There were significant differences of composition and content of volatiles among different wheat vareties.The content of volatiles(>50.35 ng/g)and terpenoids(>38%)from three susceptible varieties were both higher than those from insect-resisitant varieties,and compotent were more than Xinong822 and Xinong88.The content of ?-pinene,2-ethyl-1-hexanol and ?-farnesene had obviously difference among different varieties.5.The electroantennogram(EAG)responses of female wheat midge to 8 volatiles were tested under 4 concentrations(0.01,0.1,1 and 10?g/?L).Experimental results show that the EAG responses of adult to cis-3-hexenyl acetate and 3-hexanol were strongest,the EAG responses of adult to 2-ethyl-1-hexanol,?-cedrene and caryophyllene were weakest.In the range of test concentrations,with concentration increased,the female adult EAG response to volatiles increased accordingly.6.The response of S.mosellanaadult to 8 volatile compounds and its mixtures was related to compotent and concentration of volatiles.Female adult was significant repelled by?-farnesene in both 0.1?g/?L or 1?g/?L,but 3-hexanol(0.1 and 1?g/?L),?-pinene(0.1?g/?L),cis-3-hexenyl acetate(0.1 ?g/?L)and blend(0.1 and 0.01 ?g/?L)could attract adult significantly.