Identification and Characterization of Resistance of Three Aphid Species on Contrasting Alfalfa Cultivars.

Aphids on alfalfa ( Medicago sativa ) including Aphis craccivora Koch (cowpea aphid, CPA), Acyrthosiphon pisum Harris (pea aphid, PA) and Therioaphis trifolii Buckton (spotted alfalfa aphid, SAA) cause significant yield losses worldwide. In this experiment, the development of these three species of aphids on 16 alfalfa cultivars was compared. The results showed that the plant cultivar had a significant influence on the development of aphids as there are significant differences in the body weight of aphids reared on different alfalfa cultivars. In addition, antibiosis between the alfalfa cultivars Pegasis and Gannong NO.9 and the three species of aphids was evaluated by measuring aphid body weight and fecundity. Antixenosis was measured using choice tests, and feeding behavior was quantified using electrical penetration graphs (EPG). The Pegasis cultivar was observed to have both antibiosis and antixenosis effects with CPA, but was susceptible to PA and SAA compared with the Gannong NO.9 cultivar. CPA had less mean body weight, less fecundity, and shorter feeding time on the Pegasis cultivar, and preferred to settle on Gannong NO.9 cultivar. In contrast, Gannong NO.9 exhibits antibiosis and antixenosis to PA and SAA compared with Pegasis, as shown by lower body weight, lower fecundity and chose to settle less often, but EPG data showed that PA and SAA showed no different significance in feeding behavior between Pegasis and Gannong NO.9.