Selection Behavior Of Chinese Cabbage By Spodoptera Litura And Microplitis Similis And Analysis Of The Volatile Components Of Cabbage

Due to the characteristics of overeating,strong resistance and intermittent outbreaks,Spodoptera litura has been a serious threat to the production safety of many crops in China,especially vegetables.Herbivore-induced plant volatiles,as an important carrier of phytochemical communication,can directly or indirectly defense against herbivorous insects by regulate the relationship among plants,herbivorous insects,and natural enemy insects.Based on this,the thesis studied the feeding selection behavior of S.litura larvae on Brassica rapa which damaged by the larvae;and observed the preference behavior of S.litura and Microplitis similis,a parasitic natural enemy,to the volatiles of the damaged Chinese cabbage.The main components and release amount of the volatiles from leaves under different induction conditions were identified and analyzed by gas chromatography-mass spectrometry,and the relationship between the release amount of each component of volatiles from cabbage leaves and the selection behavior of S.litura and M.similis was also discussed.The main results are as follows:(1)The selective behaviors of S.litura and M.similis on Chinese cabbage.By observed the searching behavior of M.similis,it was found that M.similis could locate the host according to the volatiles released by Chinese cabbage during the searching process.12 h after the harmless was eaten by S.litura,the attraction of insect-induced Chinese cabbage volatiles to M.similis was significantly enhanced.The volatiles of Chinese cabbage treated with oral secretions of S.litura had a similar attracting effect on M.similis to that treated with damaged by S.litura.The volatiles of mechanically damaged Chinese cabbage and undamaged Chinese cabbage had similar attractive effects on M.similis.The results showed that the feeding behavior and host selection behavior of S.litura are affected by the induction of pest: When undamaged Chinese cabbage was fed by S.litura larvae for 24 hours,S.litura would decrease its preference for damaged leaves and showed a significant tendency to avoid volatiles from damaged leaves.(2)Analysis of volatile components of Chinese cabbage under different induction conditions.The analysis of the volatile components of Chinese cabbage undamaged and damaged by S.litura showed that the Isothiocyanates were the most volatiles released in undamaged Chinese cabbage,followed by green leaf volatiles.However,when the Chinese cabbages were damaged by S.litura and with the degree of harm increased,the relative content of the Isothiocyanates and Green Leaf Volatiles would gradually decrease,and the relative content of the Ketones and Alkanes would gradually increase.Among them,the feeding behavior of S.litura inhibited the release of E-2-hexenal and 1-Butene,4-isothiocyanato,and only that induced the release of Limonene from Chinese cabbage.The identification and analysis of the volatile components of Chinese cabbage in different treatments showed that: compared with the undamaged Chinese cabbage,there was no significant difference in the composition and release of the volatiles from the mechanically damaged Chinese cabbage.The relative content of Alkanes was increased and that of Isothiocyanates was decreased by the treatment of S.litura oral secretion which inhibited the release of Butane,1-isothiocyanato-.(3)The relationship between the release of Chinese cabbage volatiles and the selection behavior of M.similis and S.litura.The results of linear correlation analysis found that there was a significant positive correlation between the release of the Isothiocyanates and the selection rate of S.litura,and the correlations of the selection rate of S.litura with the release of the Aldehydes and Ketones were significantly negative.Among them,the release of E-2-hexenal,1-Butene,4-isothiocyanato,and Decanal are significantly positively correlated with the selection rate of S.litura,but the correlations of Limonene,Nonanal,Hexadecane,Heptadecane and Octadecane between the selection rate of S.litura were significantly negative.In the volatiles of Chinese cabbage,only the release of the Isothiocyanates had a significant positive correlation with the selection rate of M.similis.In addition,there was a significant positive correlation between the release of Limonene,Linalool,and Hexadecane volatiles and the selectivity of M.similis,and the release of E-2-hexenal and 1-Butene,4-isothiocyanato had a significant negative correlation with the selection rate of M.similis.