Comparison of Acyrthosiphon pisum probing behaviors on different alfalfa cultivars

Acyrthosiphon pisum (Harris) is a major pest of alfalfa worldwide. Here, we evaluated the resistance of eight alfalfa cultivars to A. pisum to identify resistant cultivars. The Giga-8 DC-EPG technique was used to record differences in electrical waveform patterns of probing behavior to identify cultivars with higher resistance. The frequency and average duration of EPG waveforms significantly differed among the cultivars, with eight documented waveforms (np, C, pd, E1, E2, sE2, F, and G). The longer duration of np, C, F and E1 waveforms reflected stronger resistance, whereas longer sE2 waveforms reflected weaker resistance. The resistance-related waveforms, np and C, occurred most frequently with Sardi 7, the time of the first E waveforms were the latest, duration of G waveforms and F waveforms were the longest, the feeding waveforms E2 and sE2 were the shortest, the time of reaching phloem for feeding was the latest, with notable resistance in leaf epidermis, mesophyll and phloem. The number of C waveforms occurring with Gibraltar were the least, duration of np waveforms was short, feeding waveforms were long, time to reach the phloem for feeding was early, and the resistance was not pronounced in various tissues. After comprehensive evaluation, the resistance levels of 8 alfalfa cultivars were as follows: High resistance, Sardi 7; Resistance, Zhongcao No. 3, Derby, WL319HQ; Low resistance, Golden Empress, Algonquin, Zhaodong; Susceptible, Gibraltar. In conclusion, evaluation of cultivar resistance to aphids can provide baseline data for selecting and planting cultivars with high local resistance.