Abstract:
Annual medics (Medicago spp.) with resistance to spotted alfalfa aphid (Therioaphis trifolii (Monell) fm. maculata) (SAA) are progressively replacing older susceptible cultivars in new sowings in Australian pastures. Six lines and cultivars from the species M. truncatula and M. littoralis with varying degrees of SAA resistance were studied for their effect on SAA survival, development and reproduction.Antibiosis in the form of decreased nymph and adult survival, increased developmental times and decreased nymph production per adult and production rate were detected. In the resistant lines tested, Sephi and 2-243 had very high levels of antibiosis to SAA: sufficient to prevent any nett multiplication of SAA. Two less resistant lines, Parabinga and SA 12591, also had significant antibiosis to SAA compared to the susceptible cultivars Harbinger and Borung, but aphid survival and multiplication were still moderately high. Behavioural patterns suggest antixenosis is insignificant as a resistance mechanism in all these lines in a no-choice situation.