Tripping of alfalfa and manipulation of pollinator foraging behavior by flowers

[Objective] Elucidating the tripping mechanism and the role and status of flowers in this process are of great significant to explore the diverse pollen dispersal mechanism. [Methods] Alfalfa (Medicago sativa L.)‘Xinmu No. 4’ was used as the research object to observe the flower tripping phenomenon and pollinator visiting behavior, pollen transfer control experiment, and anatomical observation of flower structure. [Results] The specialized structure of wings and keel edge were nested with each other and form the touch-sensitive flower structure of alfalfa. The “sensitiveness” structure not only had high selectivity to pollinators, but also could manipulate pollinators􀆳 visiting behavior by changing the location of honey hole before and after tripping. Once the keel flap was tripped, about 90% of the pollen in the anther was dispersed, and the gynostemium did not return to the original position. The flower closed on the same day, or it continued to open 5-6 d, which was a one-time pollen release mechanism. Tripping efficiency of insects, being not related to the insect􀆳s size, determined the tripping contribution rate together with its visiting frequency. The insect􀆳s second visiting did not increase the removing of residual pollen from anthers and pollen deposition on stigma. [Conclusion] The special flower structure and its regulation of pollinators􀆳 foraging behavior promote the occurrence of tripping phenomenon, and benefits the male fitness in alfalfa.