| Horned gallnut is induced by Schlechtendalia chinensis (Bell) on the leaflets of itsprimary host Rhus chinensis Mill, and is also the result of a close relationship between S.chinensis and its host plant R. Chinensis, and reflects their long-term coevolution. But thereis a few of researches about their coevolution relationship. This paper mainly regards S.Chinensis, R. Chinensis, and horned gallnut as the research object. By the studies about thedynamic growth of horned gallnut, physiological changes of R. Chinensis, clone dynamics ofS. Chinensis and their honeydew excretion, we have preliminarily understood the relationshipbetween gall development and aphids clone size, the relationship between aphid density andwing dimorphism, the differences of galling aphid in antennal sensilla and honeydew excretion,and R. Chinensis’ response to S. Chinensis’stimulation. This research have laid thegroundwork for future research on the mechanisms of gall formation and wing dimorphism,and also provided powerful evidence for coevolution researches between S. chinensis and R.Chinensis. The main conclusions are as follows:(1) The study on gall development and clone dynamics of the galling aphid S. chinensisWe found that: Gall-size changes occurred in four stages: a first slow growth period, a fastgrowth period, a second slow growth period and a growth reduction period. Gall volume andsurface area increased abruptly towards the end of July, peaking during October, in parallelwith an increase in aphid clone size, from one individual to more than10000aphids per gall.Clear changes were seen in the clone dynamics of S. chinensis. Fundatrix began to producefirst-generation apterous fundatrigenia during late May to early June. Second-generationapterous fundatrigenia appeared at the start of July. Alate fundatrigeniae with wing pads firstappeared at the end of August, but accounted for <1%of the individuals in the galls. Adultalate fundatrigeniae first appeared at the start of October. Abrupt changes in aphid density and crowding might trigger the induction of alate morphs in the galls. Of the eight gall propertiesthat we recorded, gall volume was the most accurate measure of gall fitness.(2) Comparison and analysis of the antennal sensilla of morphs of the galling aphidUsing scanning electron microscopy, we compared and analyzed the ultrastructure, type,distribution and number of antennal sensilla of morphs of the aphid S. chinensis. The resultsshowed that S. chinensis has four types of antennal sensillum: trichoid sensilla, primaryrhinaria, sensory projections and secondary rhinaria, which varied in their distribution andappearance on the antenna of the different morphs. We suggest that these differences detectedare related to the habitat of the particular morph, its main form of behavior (e.g. Feeding,migration, and host selection).(3) Host Plant photosynthetic, nutrition and ABA response to aphid stimulation duringhorned gallnut developmentWe studied the changes of amino acid, chlorophyll and abscisic acid in horned gallnuts(HG), leaves with galls (LWG) and leaves without galls (LNG) throughout the period of galldevelopment. The result showed that there were chlorophyll a and b in HG. Although thechlorophyll content in HG was obviously lower than that in leaves, both chlorophyll changregularities were basically the same. That showed HG had a certain capacity of photosynthesis,and was a kind of metamorphosed leaf.The chang of abscisic acid content in HG was a single-peak curve which was graduallyincreased and declined at the late stage of gall development. The abscisic acid content in HGwas obviously lower than that in leaves of R. Chinensis during the process of gall development.Abscisic acid have effects of inhibiting growth promotion induced by gibberellic acid andcytokinin, and is related to leaf senescence, fruit abscission etc. The low content of abscisicacid in HG was probably due to a substance which was released by S. Chinensis and thissubstance inhibited the abscisic acid synthesis in HG. The normal growth of leaf wing may beinterfered by the low content of abscisic acid in HG and form a metamorphosed leaf. Withoutthe inhibition of abscisic acid, leaf wing grew excessively, and finally formed the peculiar shape of gall. The increase of abscisic acid content in HG was a signal to suppress gall growth,and was also a portent of gall maturity. The signal may be transmitted to S. Chinensis, andhave an impact on the wing dimorphism which made preparation for their migration.The composition of amino acid in HG, LWG and LNG was the same, all containing17kinds of the same amino acid, but the content of them is significantly different. The amino acidcontent in galled leaves (LWG) was higher than that in ungalled leaves (LNG), and that inhorned gallnut (HG) was obviously the lowest. That showed that the amino acid content inleaves was increase after the host plant stimulated by aphids, and formed the nutrition sink forthe galls. This result support the " source-sink hypothesis".(4) A preliminary study on Colletorichum from horned gallnutWhen studied gall development and clone dynamics of the galling aphid, we isolated apathogenic fungus from horned gallnut. Its damage status and mycelium characters on gall andmydium are described, and its morphological and molecular biological characteristics wereidentified. The pathogenic fungi is Colletorichum gloeosporioides (Penz.) Sacc belongs toMelanconiales (Deuteromycotina: Coelomycetes). |
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