Abstract: 【Aim】 To clarify the feeding behaviors of Therioaphis trifolii on different cultivars of alfalfa (Medicago sativa), to ascertain the anti-aphid factors and insect resistance sites, and to screen out the M. sativa cultivars resistant to aphids. 【Methods】 The feeding behaviors of T. trifolii adults on 10 alfalfa cultivars were recorded using electrical penetration graph (EPG) technology, appropriate EPG parameters were selected based on clustering analysis and aphid resistance was evaluated with these EPG parameters. 【Results】 T. trifolii adults fed on different alfalfa cultivars showed eight waveforms including np waveform, pd waveform, A waveform, B waveform, C waveform, E waveform, F waveform and G waveform, and the total duration of E waveform, F waveform and G waveform of T. trifolii adults on different alfalfa cultivars showed significant differences. During the 5 h test period, the duration of E waveform on Aohan was the longest, followed by that on Golden Empress and Zhongmu No.3, and that on Caoyuan No.2 and Algonquin was the shortest. The total duration of F waveform on Zhungeer, Algonquin and Golden Empress was the longest, and that on Aohan, Derby and Caoyuan No. 2 was the shortest, suggesting that the formers have strong mechanical resistance and the latters have weak mechanical resistance. Using the duration of the first probe, total duration of probe wave, total duration of F waveform, total duration of C waveform, and total duration of E waveform as indices for cluster analysis, 10 alfalfa cultivars were clustered into 3 categories: Algonquin, Caoyuan No. 2, WL168HQ, Derby, Zhongmu No. 2 and Xinmu No. 2 in category I, Golden Empress, Zhongmu No. 3 and Zhungeer in category II, and Aohan in category III. 【Conclusion】 The feeding behaviors of T. trifolii adults on different alfalfa cultivars are different. The alfalfa cultivars Caoyuan No. 2, Algonquin and WL168HQ show resistance to T. trifolii adults at the levels of leaf epidermis, mesophyll and phloem, and Golden Empress shows resistance to T. trifolii adults when leaf epidermis and mesophyll are pierced. T. trifolii adults can pierce and suck for a long time on Aohan, so Aohan shows the lowest resistance to T. trifolii adults. This study provides a theoretical basis for further exploring the mechanisms of alfalfa resistance to insects and the integrated control of aphids.

Key words: Medicago sativa, Therioaphis trifolii, aphid resistance, feeding behavior, electrical penetration graph, cultivar selection