Research On Mechanisms Of Dominant Pollinator Visiting Xanthoceras Sorbifolia

During long-term evolution,the flower structure of entomophilous plants is developing conducively towards the direction of cross-pollination,and the external morphology of insects towards the direction of collecting nectar and pollen.Therefore,there are close mutualistic relationship between entomophilous plants and pollinators.With the rapid development of chemical technology,flower plant and pollinator interaction,in the perspective from flower volatile,becomes a hot topic to reveal the mechanism of insects visiting flowers.The fruit of Xanthoceras sorbifolia is important due to its high medicinal value,industrial value and ornamental value,but its yield is lower.Therefore,it is urgent to find a way which can improve the production of the fruits.Increasing pollination efficiency of Xanthoceras sorbifolia is necessary.This study was conducted to identify dominant pollinator,floral volatiles components of Xanthoceras sorbifolia,and the relationship between them,which not only provide a solid foundation for understanding the relationship of entomophilous plants and pollinator,but also helps to further develop insects' attractants and industrialization of artificial reproduction,thus improving the development of the related industries of Xanthoceras sorbifolia.In this study,species of pollinator were investigated,morphological features of flower was measured,and volatiles components of Xanthoceras sorbifolia flowers were determined.And then,the relationship between dominant pollinator and floral volatiles was analyzed by using the field trapping method.Finally,types of antennal sensilla of dominant pollinator were examined with scanning electronic microscopy(SEM).The main conclusions were as follows:1.A total number of 1799 pollinators were collected and identified in 2016 and 2017,which belong to 5 orders,26 families,54 genera and 73 species.Among them,1120 insects were Diptera belonging to 6 families,18 genera and 26 species,and took a percentage at 62.257% of the total number of dominant pollinators;407 were Coleoptera insects belonging to 6 families,12 genera and 13 species,accounting for 22.624%;156 were Hymenoptera insects belonging to 7 families,13 genera and 23 species,accounting for 8.671%;78 were Lepidoptera insects belonging to 3 families,7 genera and 7 species,accounting for 4.336%;38 were Hemiptera insects belonging to 4 families,4 genera and 4 species,accounting for 2.112%.According to the analysis on the number of flower-visiting insects,Dominant pollinator of Xanthoceras sorbifolia was Bibio rufiventris.There were 858 individuals to be collected,accounting for 47.693% of the total number of pollinators.In 2016,there were 443 individuals,accounting for 47.892% of the total number of pollinators.Among them,there were 234 males and 209 females,accounting for 25.297% and 22.595% respectively.In 2017,there were 415 individuals,accounting for 47.483%.There were 247 males and 168 females,accounting for 28.261% and 19.222% respectively of the total number of pollinator in 2017.2.Characteristics of Xanthoceras sorbifolia flowers were measured,with 10 to 40 flowers per inflorescence.Results showed that staminate flowers and hermaphrodite flowers were similar in shape and size.There were 5 Star shape petals,each petal was obovate,white,thin texture,the initial medial base with yellow-green halo spot,but with the development of the flower,the color of the halo spot gradually changed from yellow-green to deep purple-red.The volatiles components of Xanthoceras sorbifolia flowers were determined by using gas chromatography-mass spectrometer in this study.The results showed that there were 44 kinds of flowers volatiles in all,and 1-Octen-3-ol,Nonanal,Methyl salicylate,1-Octanol,Farnesene,(E)-2-Hexen-1-ol,(Z)-3-Hexen-1-ol,(E)-2-Hexenal,(E,Z)-2,6-Nonadienal,Octanal,(E)-2-Nonenal,Benzaldehyde,6-Methyl-5-hepten-2-one,Tridecane,and Cyclocitral were the major components of flowers volatiles.3.The results of field trap experiment showed that 1-Octen-3-ol,1-Octanol,Farnesene,(E)-2-Hexen-1-ol,(E,Z)-2,6-Nonadienal,(E)-2-Nonenal,6-Methyl-5-hepten-2-one had significantly attractant effect on Bibio rufiventris,and such effect was species-specific.The attractant effect of(E,Z)-2,6-Nonadienal and(E)-2-Nonenal on the female adults was higher,and attractant effects of 1-Octen-3-ol,1-Octanol,Farnesene,6-Methyl-5-hepten-2-one on the male adults were higher.Besides,(E)-2-Hexen-1-ol had equal attractant effect on both female and male adults.4.The results showed that antennae of female and male Bibio rufiventris both were made of three parts,a proximal scape(Sc),a pedicel(P)and a flagellum with 8 flagellomeres(F1-F8).The total antennae lengths of female and male were 862.556 ?m � 78.662 ?m and 880.361 ?m � 83.253 ?m respectively.The length of antennae for each segments of female and male adults were almost equal,except eighth flagellomeres.There were four different types to be identified in both female and male antennae,including B?hm bristles(Bb),sensilla chaetica(Sc),sensilla trichodea(St)and sensilla basiconca(Sb).Among them,the female had six different subtypes of sensilla: B?hm bristles(Bb),sensilla chaetica(Sc),sensilla trichodea type 2(St.2),sensilla basiconca type 1(Sb.1),sensilla basiconca type 2(Sb.2),and sensilla basiconca type 4(Sb.4).The male had five different subtypes of sensilla: B?hm bristles(Bb),sensilla chaetica(Sc),sensilla trichodea type 1(St.1),sensilla basiconca type 2(Sb.2),and sensilla basiconca type 3(Sb.3).In summary,the interaction between the volatiles of Xanthoceras sorbifolia and its dominant pollinators was examined by analyzing flower characteristics(external morphology,odorant)and the olfactory characteristics(antennal sensilla)of Bibio rufiventris.These results provide intrinsic mechanism on Bibio rufiventris visiting Xanthoceras sorbifolia,and suggest a theoretical basis for further exploring the co-evolution between Xanthoceras sorbifolia and pollinators.