Study On Chemical Communications Among Tea Plant,Iragoides Fasciata Moore(Lepidoptera:Eucleidae),Chaetexorista Palpis Chao(Diptera:Tachinidae)

The tea slug moth, Iragoides fasciata Moore (Lepidoptera:Limacodidae), which can break out under certain conditions, is one of the major insect pests of tea (Camellia sinensis L.(Ericales:Theaceae)). It not only causes reduction of tea output, and even result in death of tea plant, but also seriously hampers field operations of tea farmers. Currently, the control of tea slug moth mainly rely on chemical control, In view of the negative impact of chemical pesticides, new control technologies of other insect pest based on researches on chemical ecology have been developed in recent years, and more and more scientists pay attention on it.C. palpis Chao (Diptera:Tachinidae), a newly discovered parasitic natural enemy based on our field and laboratory observation is an important parasitic natural enemy of tea slug moth.Here, Chemical communications among tea plant, tea slug moth, Chaetexorista palpis Chao were investigated to provide a theoretical basis for the control of tea slug moth.Observed in the tea garden, we found that the number of C. palpis in the tea plantations where tea plants were damaged by tea slug moth was significantly more than those undamaged. We speculate that tea plant would release specific signal substances which play a key role in host location (especially long distance) by C. palpis. In order to confirm this conjecture, the effect of the damaging of tea slug moth on the volatile organic compounds (VOCs) of tea plant was studied. VOCs from the undamaged and damaged tea plants were collected by simultaneous distillation extraction and dynamic headspace, then analyzed by gas chromatography/mass spectrometry (GC-MS). The results of the foraier showed that a total of sixty-three components, mainly esters, alcohols, hydrocarbons, ketones, heterocyclic compounds, aldehydes, organic acids and ethers were identified in the undamaged twigs and leaves, and the relative content of hydrocarbons was19.05%, while that from the damaged ones increased to26.79%, and the relative content of cis-nerolidol, cedar alcohol, dibutyl phthalate and phthalic acid was significantly increased. Furthermore, thirty-two new compounds were identified in the damaged ones, including ten esters, five alcohols, five olefins, four heterocyclics, three aromatic hydrocarbons, one alkane, one ketone and one aldehyde. The latter results indicated that a total of seventy-four components were identified in the undamaged twigs and leaves, and the composition of volatile compounds was similar to the former. Compared with the undamaged twigs and leaves, the number and relative content of ethers, aldehydes, and hydrocarbons changed evidently, while those of alcohols, heterocyclic compounds, ethers and organic acid compounds had little change. After damage, the relative content of4-cymene, pinene,1-ethyl-2,4-dimethylphenoxy,4-ethyltoluene, toluene-ethyl-6-methyl-heptene[5]ketone[2] and1,2,4-trimethylbenzene increased significantly, fifty-four new compounds were founded in the damaged ones, including of fourteen alkenes, twelve aromatic hydrocarbons, eight esters, eight alkanes, five ketones, three alcohols, two aldehydes, one heterocyclic and one organic acid. It is worth noting that the number and relative content of terpenoids significantly changed, suggesting that these compounds maybe play an important role on the host finding by C. palpis.The results can lay a foundation for screening infochemicals which can be used as a lure for natural enemies of insects and applied to control I.fasciata MooreIn order to screen attractants for tea slug moth and C. palpis, Electroantennogram responses to a wide range of plant volatile compounds that have been identified in tea plants were recorded from males and females of the tea slug moth and C. palpis. The responses to26compounds, belonging to several chemical classes, and two mixtures were evaluated for tea slug moth, while27compounds for C. palpis. The results showed that most of the compounds can elicit significant electrophysiological responses in both tea slug moth and C. palpis. There were significant different electroantennogram responses to the different chemicals, different types of compounds,as well as significantly different responses according to gender in these two species. In general, the antennae of males of tea slug moth were more sensitive, and responded more strongly, to most of the compounds, while it was just the reverse in C. palpis, Responses to sesquiterpenoids were lower in both males and females of tea slug moth. Dose-dependent response studies indicated differences in response between genders and concentrations, suggesting the existence of sexual dimorphism in tea slug moth. In C. palpis, females responed more strongly to cis-3-hexene-1-alcohol, while males to cis-3-hexenyl acetate. Compounds belonging to green leaf volatiles class elicited significantly greater responses in both males and females in tea slug moth and C. palpis. we speculated that they might be important clues in host-plant selection by this oligophagous species and its parasitic natural enemy.In order to explain the differences of electrophysioiogical responses of the male and female of tea slug moth to some plant volatiles associated with tea, the antenna and antennal sensilla of tea slug moth were investigated by scanning electron microscopy. Eight types of antennal sensilla were found in the antenna: sensilla trichodea(ST), sensilla basiconica(SB), sensilla chaetica (SC), sensilla coeloconica (SCo), bohm bristles (BB), sensilla squamiformiaa (SS), sensilla furcatea(SF), sensilla styloconica(SST). Two types of antennal sensilla,sensilla squamiformiaa and sensilla furcatea were only found in female.There were no obvious sexual differences in sensillum morphology for the other six types of antennal sensilla, but a certain differences in distribution and quantity for these types. This study provided ultrastructural evidence for the sexual morphological dimorphism of the antenna. Obvious differences in the number of sensilla chaetica between male and female may be serve as the explanation for the differences of electrophysiological responses of the male and female of tea slug moth to some plant volatiles associated with tea.