Settling behaviour and reproductive potential of the green peach aphid Myzus persicae on peach varieties and a related wild Prunus

Discovery in the late seventies of resistance to the green peach aphid Myzu s persicae (Sulzer) (Homoptera: Aphididae) in Prunus species was based on s creening in the field or in greenhouses with natural aphid populations. Her e, we assess the impact of these wild and domesticated peach trees on the b ehaviour, development, reproductive performance and demography of cloned ap hids under controlled light and temperature. Four peach varieties, i.e., Ru bira, Weeping Flower Peach, Summergrand and Male konare and the clone P1908 of the related species Prunus davidiana were tested against the highly sus ceptible cultivar GF305. Besides a variability in the performance of aphids among experiments, our results showed that (i) distinct mechanisms were in volved in the sources of resistance studied and (ii) the ranking of the gen otypes on their resistance/susceptibility status remained roughly stable th roughout the experiments. Observations on the settling behaviour of first i nstar nymphs demonstrated antixenosis components in the resistance conferre d by Rubira and Weeping Flower Peach. Nymphs began to leave the plants afte r a short exposure (19-21 h) and no aphid was left after 4 days. Nymphal mo rtality remained rather low (16%) compared to the repellent effect on aphid s of both genotypes. Nymphs disappeared from Weeping Flower Peach significa ntly earlier than from Rubira. Summergrand, Male konare and P. davidiana cl one P1908 were accepted as host plants by aphids. On P. davidiana, decrease d fecundity and intrinsic rate of natural increase (r(m) = 0.20, averaged o n all experiments) were clear expression of antibiosis. In addition, the me an length of the mature embryos within the gonads of the females on the day of adult moult was negatively correlated with the total number of embryos, providing evidence that aphids on this genotype lacked sufficient ressourc es to be directed both towards production and growth of embryos. Compared t o the most susceptible cultivar GF305 (r(m) = 0.36), Summergrand(r(m) = 0.2 6) and Male konare (r(m) = 0.28) had, to a lesser extent, a negative impact on nymph production and rate of increase.