Host-correlated morphological variation of Myzus persicae (Hemiptera : Aphididae) populations in Greece

Morphological variation in nine characters of 157 clones of Myzus persicae (Sulzer) was examined by multivariate analysis. The clones were collected f rom peach, Prunus persica, the primary host and the secondary hosts tobacco , Nicotiana tabacum, cabbage, Brassica oleracea, sugarbeet, Beta vulgaris a nd pepper Capsicum annuum. The 156 clones originated from various regions o f Greece, both in the north, where a large part of the population has an an nual bisexual generation on peach, and in more southerly regions, where pop ulations are predominantly unisexual. One clone was collected from tobacco in Caserta, Italy. All clones were laboratory-reared on potato. Canonical v ariate analysis, hierarchical cluster analysis and a non-parametric classif ication tree method both revealed morphological differences associated with the host-plant on which they were collected. The scores of the first two c anonical variates separated the tobacco-feeding clones from those originati ng from other secondary host-plants. However, in tobacco-growing areas the tobacco-feeding form predominated in spring populations on peach, and was s ometimes found on other secondary hosts. In addition, using cluster analysi s, the clones from tobacco which were sampled in the most southeasterly reg ion showed a relatively large phenotypic distance from those collected furt her north and west. Moreover, clonal phenotypes were affected both by host plant and by long-term parthenogenetic rearing. However, in spite of these effects, the tobacco form was generally distinguishable from aphids origina ting from other hosts, indicating that the difference must have a genetic b asis. In separate analyses of the clones originating from secondary hosts n o association was found between morphology and either life cycle category o r colour. Discriminant analysis showed that 89% of 1723 specimens could be correctly classified into the two groups.