| Bactrocra dorsalis is an important quarantine pest with a variety of fruitsand vegetables such as bananas, citrus, mango and chili pepper as its hosts. Itdamages the hosts mainly by female egglayin in the peel of the fruit and the larvalfeeding on the fruit. Such damages not only cause the fruit rot but also lead to ayellow coloration and fall off before the fruits become ripe. These damages seriouslyaffect the yield and quality of the fruits. It make the fruits even completely lose theirfood value, causing serious economic losses. Trapping and killing B. dorsalis usingtrapping agents is a both effective and environmentally friendly control measure.Methyl eugenol currently used can only lure the males. Because of the ways that B.dorsalis causes the damages it is difficult to control B. dorsalis by trapping agentwhile chemical prevention and treatment are inconsistent with the concept of greenfruit production. Development female lure has become a new biocontrol idea in thecontrol of B. dorsalis. This thesis reported the study on the injury characteristics of B.dorsalis in four different citrus groups and the olfaction mechanisms in order toprovide basic information for the development of female lure. The results weresummarized as follows:1. Research on biological characteristics of the B. dorsalis fedon differentannual citrus fruitsThe changes in life cycle of B. dorsalis after fed on four common varieties ofcitrus fruit for two years were observed and studied. The results showed thatthe larval duration was negatively correlated with the pupal duration with acorrelation coefficient of-0.812. Generally, the survival rates of B. dorsalis withlight body weight and heavy puparium weight or with heavy body weight and lightpuparium weight were not high. The survival rate was high when the insects withmoderate puparium weight (0.95-1.0mg) or the body weight (12-15mg). Thesurvival rates of B. dorsalis raised on Fortunulla "Jinju" in the years of2009and2010were95%and80%, respectively, which were highest among seven different citrus varieties. It was followed by the variety of Citrus reticulata such as citrus andthe local early citrus. The survival rates of B. dorsalis raised on Citrophorum "C.limon" and Miyagawa were the minimum. The sex ratio of B. dorsalis raised on C.reticulata and Miscellaneous citrus were homogeneous. The sex ratios were greaterthan one. The annual female number of Ponkan and Mayagawa was higher than themale number, but the annual male number of C. grandis "Huyou" was higher thanthe female number. According to the larval duration or the puparium and larval bodyweight, Jinju appears to be a suitable host for fruit fly growth. However, the lemonwas not suitable fruit. Combined with the life table, B. dorsalis fed with C. grandisshowedits net reproductive rate (R0) of35.9333, intrinsic rate of increase (rm) of0.0779and cycle growth rate (λ) of1.0811. In addition, the populations doublingtime (DT) was also the shortest. In contrast, the insects fed on lemon showed R0of13.5167, rmof0.0549and λ of1.0564; rmis the least, and T and DT were largest.2. Cloning, expression and purification of odorant binding protein2from B.dorsalisIn this study we cloned odorant binding protein gene BdorOBP2of B. dorsalis.Its GenBank accession number is KC773766. Sequence analysis showed that theORF of BdorOBP2is447bp, encoding148amino acid residues. Multiple sequencealignments showed the highest sequence similarity of BdorOBP2with those ofDrosophila melanogaster and D. virilis. Phylogenetic analysis showed thatBdorOBP2was closely related to those of dipteran species, especially DantOBP2. Inaddition, we established BdorOBP2prokaryotic expression system and expressed theprotein for fluorescence binding assays.3. The binding characteristics of BdorOBP2from B. doticsrsalis with22volatile odorsFluorescence competitive binding experiment results showed that BdorOBP2hadstrong binding capacity against aldehydes and esters, and have weak bindingcapacity against alcohols and vinyl compounds. In our binding studies with estercompounds, most of the odor volatiles can reduce the binding rate of1-NPN withBdorOBP2by more than50%except for cis-3-hexenyl acetate. Foraldehydescompounds, most of the odor volatiles examined (except for acetaldehyde)can reduce the binding rate of1-NPN with BdorOBP2by more than50%.. Benzaldehyd and3,4-dimethoxybenzaldehyd showed the strongest binding ability,and they can reduce the value of the relative fluorescence competition to10%or less.For aldehyde class of compounds, in addition to acetaldehyde, almost all the bindingrates of1-NPN with BdorOBP2were below50%. Among these compounds,benzaldehyde and3,4-dimethoxy benzaldehyde showed the strongest binding ability,and they can reduce the relative competition in the fluorescence value to10%orless. The binding capability of BdorOBP2and beta-ionone was also strong. It canreduce the rate of1-NPN with BdorOBP2below to7%. It indicated that theseimportant volatile odors play an important role in the process of positioning,oviposition and infestation of B. dorsalis.4. Electroantennogram responses of B. dorsalis to18volatilesB. dorsalis was highly responsive to the majority of esters and aldehydes,which are consistent with the results from the binding assays. For example, B.dorsalis females can generate strong electrical physiological reactivity ontrans-2-hexenal and benzaldehyde, but the males were able to produce a strongresponse on methyl salicylatein. Fluorescent decanal was a good ligand in bindingassays, but it can not lead to strong electrophysiological responses in EAG trials.This is probably because the EAG test measures the antennal sensilla overall activity,and BdorOBP2is just a protein present in the fruit fly antennal sensilla. Nevertheless,there are many insect sensor OBPs which show the division of labors in the olfactorysystem. Different OBPs are expected to respond to different odorants differently. |
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