| This study was based on a tritrophic system including cotton Gossypium hirsutum, cotton bollworm Helicoverpa armigera, and parasitoid Microplitis mediator, the behavioral responses of M. mediator to different instars cotton bollworm (CBW) larvae and cotton plant damaged by different instars CBW larvae were studied, cotton plant volatiles induced by CBW larvae were collected and analyzed in the laboratory. Furthermore, by using electronic nose zNoseTM for the first time, the cotton plant common volatiles library was constructed. We also got the fingerprint database of cotton plant infested by CBW larvae, and the real-time release rhythm ofβ-pinene andβ-myrcene from cotton plant damaged by CBW larvae treatment were monitored. The major results are listed as follows:1. The taxis responses of M. mediator to different instars CBW larvae and cotton plant damaged by different instars CBW larvae were measured in a Y-shaped olfactometer. The result showed that 3rd, 4th and 5th instar CBW larvae had non-significant attraction for M. mediator, while 1st and 2nd instar CBW larvae had significant attraction for M. mediator, but there was no significant differences between them. Among the behavioral responses of M. mediator to cotton plants damaged by different instars CBW larvae, there are two kinds of treatment, wiping out CBW larvae from cotton plant damaged by CBW larvae (dislodge larvae treatment) and damaged cotton plants +larval CBW (retain larvae treatment). The results revealed that both cotton plant damaged by CBW larvae and healthy cotton plant were attractive to M. mediator, yet there was no significant differences between them. As for damaged cotton plants + larval CBW, the volatiles from cotton plant infested by CBW larvae were more attractive to M. mediator than those of healthy plant, and there existed significant differences between them. There was notable differences among different instars, The relative selective preferences order was plant infested by 5th instar larvae of CBW> plant infested by 2nd and 4th instar larvae of CBW> Plant infested by 1st and 3rd instar larvae of CBW.2. The qualitative and quantitative analyses of the cotton plant volatiles induced by different instars CBW larvae were conducted by using GC-MS, the results showed that the kinds and contents of volatiles from cotton plant infested by CBW larvae were more than those of healthy plant. About 30 kinds of volatiles were qualitatively identified, healthy plant did not detect the release ofβ-myrcene and 1-octanol, 3,7-dimethyl-, but cotton plant damaged by CBW larvae could be detected. The type of volatiles from cotton plant damaged by CBW larvae (dislodge larvae treatment) were the same as those of holding CBW larvae treatment, there was difference in the aspect of content. The content of volatiles from cotton plants infested by CBW larvae were markedly higher than healthy plants, this stated that CBW larvae had striking induction to cotton plant volatiles. Moreover, compared with cotton plant damaged by CBW larvae (dislodge larvae treatment), the contents ofα-pinene,β-pinene,β-myrcene, 3-hexen-1-ol, acetate, (E)-and (D)-limonene in retaining CBW larvae treatment were extraordinary higher, and there was significant differences between them.3. By using electronic nose for the first time, cotton plant common volatile compounds were qualitative analyzed in laboratory. We determined relative retention index for each type of compounds, then constructed the cotton plant common volatiles library. based on the library, the volatiles from cotton plant infested by CBW larvae were collected, and we also got the fingerprint database of cotton plant damaged by CBW larvae. Comparing the healthy plant with cotton plant infested by CBW larvae, it was found that both the kinds and contents of volatiles from cotton plant damaged by CBW larvae treatment were notably higher than those of control (no treatment). Furthermore, the contents of volatiles from cotton plant damaged by CBW larvae (retaining larvae treatment) were significantly higher than those of cotton plant damaged by CBW larvae (dislodge larvae treatment), which was basically the same as the results obtained from GC-MS.4. Moreover, by using electronic nose, the real-time release rhythm ofβ-pinene andβ-myrcene from cotton plant infested by CBW larvae treatment were monitored. The results showed that when cotton plant damaged by CBW larvae for two hours,β-pinene released significantly increased compared with the control. However, there was no difference in the contents ofβ-myrcene between the cotton plant damaged by CBW for two hours and healthy plant. After invested for 2-4 hours, theβ-myrcene contents markedly increased. And after 6-8 hours, the contents ofβ-pinene andβ-myrcene reached their maximum release respectively, and then slow down, but still maintained a high level of release.
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