Research On The Effects Of Flora Scent Of Medicago Sativa On Its Dominant Flower-visiting Insects

Plants and flowering-visiting insects are two important components in the terrestrial ecosystems.During long-term co-evolution,they interact to form an inseparably muturalistic relationships,which is important for maintaining biodiversity and improving plant reproduction.Therefore,the interaction between plants and flowering-visiting insects has increasingly paid more attention for ecologists and evolutionalsit.In recent years,with the rapid develoent of chemical ecology,the role of flower volatiles on the interactions between plants and flower-visiting insects is increasingly recognized,which is important for mechanistic understanding the evolution of plants and flowering-visiting insects.Alfalfa(Medicago sativa L.)is one of the most important economic forages in China,and the develoent of related products is severely restricted because of low seed production.M.sativa is a cross-pollination plant species,and the propagation of pollen mainly depends on flowering-visiting insects.However,substantial knowledge on the interactions between alfalfa and its flower-visitng insects from a perspective of floral volatiles is still lacking.Thus,in this study,dominant species of flower-visiting insects in M.sativa at Northeastern China was investigatted,the behavioral changes of dominant flower-visiting insects were observed,the composition and content of floral volatiles were identified,and the relationships between visiting behavior of dominant species and the main floral volatiles were further analyzed.It concluded as follows:1.Through two years of investigation on visiting-flower insects of M.sativa,a total of 137 insect species collected in this study,belonging to seven orders:Hymenoptera,Diptera,Luehdorfia,Coleoptera,Hemiptera,Neuroptera and Odonata.ong them,ratio of Megachile.manchuriana abundance to total insect abundance was10.72%,thereby indicating that M.manchuriana is considered as the dominant flower-visiting insect species of M.sativa in the experimental site.2.Visiting behavior of the M.manchuriana showed daily changes.For inflorescences,the visiting number of M.manchuriana during the period of 15:00-15:30 was significantly higher than that of 9:00-9:30 and 12:00-12:30.For the florets of each inflorescence,the visiting number of M.manchuriana and visiting time in the period of 15:00-15:30 were significantly higher than that of 9:00-9:30 and 12:00-12:30.3.65 compounds in 9 categories of floral volatiles in M.sativa were found.The main floral volatiles of M.sativa were 3-Octanone(35.08%),Hexanal(14.74%),2-Hexenal(14.18%),Hexanal(6.43%),1-Octen-3-one(5.08%),3-Octanol(1.9%),and(E,E)-2,4-Heptadienal(1.23%).And moreover,daily changes of M.sativa floral volatiles were further ananlyzed,and found that the relative content of(E)-2-Pentenal gradually increased with the time,while the relative contents of Methyl salicylate,(Z)-2-Penten-1-ol,1-Penten-3-ol and 2-ethyl Furan gradually decreased.In addition,certain compounds appear in special time periods,such as(E,Z)-2,6-Nonadienal at9:00-9:30,Hexyl acetate appears at 12:00-12:30,and Pentanol appears at 15:00-15:30.4.By bioassay experiment,the results showed that NENUa had clear repellent effects on M.manchuriana at a concentration of 100 ppm,but significant attractive effects at a concentration of 1000 ppm.NENUf attracted more M.manchuriana at concentrations of 100 ppm and 10000 ppm.While NENUb,NENUc,NENUe,NENUg had repellent effects on M.manchuriana,and this effect depends on the compound concentration.5.Daily change of visiting behavior of M.manchuriana was correlated with the light intensity and the daily emission floral volatiles in M.sativa.The light intensity during the period of 15:00-15:30 was significantly lower than that of 9:00-9:30 and12:00-12:30.Meanwhile,the relative content of(E)-2-Pentenal increased significantly,but the relative content of Methyl salicylate decreased significantly.These changes in light intensity and the emission of M.sativa compounds may be important factors in mediating the daily changes of visiting behavior of M.manchuriana.However,detailed mechanisms need to be further explored.In summary,the preliminary study on the relationship between floral volatiles of M.sativa and its dominant flower-visiting insect at Northeastern China was conducted,and found that M.manchuriana is the dominant flower-visiting insect species,and NENUa and NENUf emitted from M.sativa flowers have attractive effects on M.manchuriana.The daily changes in visiting behavior of M.manchuriana may be related to the changes in floral volatile emission and light intensity.These findings provide a cental research basis for further enriching the theory of the muturalistic interactions between plants and flower-visiting insects.It also suggests that the findings are important guidance for the breeding of key pollinators and the development of attractive lure in the improvement of M.sativa seed production.