Host specificity and speciation

Abstract

Most aphids are autoecious (Figure 3.1), living on one or a few species of a particular genus of plants (Eastop, 1973). About 10% are heteroecious (Figure 3.1), spending autumn, winter and spring on a primary host plant, and the summer on a secondary host plant(s), which is rarely closely related to the primary host. For example the primary host of the rosy apple aphid, Dysaphis plataginea, is apple (Rosaceae) and its secondary host is plantain (Plantago lanceolata, Plantaginaceae); for the currant-yellow rattle aphid, Hyperomyzus rhinanthi, it is red currant (Ribes rubrum, Grossulariaceae) and greater yellow rattle (Rhinanthus major, Scrophulariaceae), respectively. Although heteroecious species are classified as polyphagous it is noteworthy that most of them live on one species of plant at a time, i.e. they are sequentially monophagous. The type of heteroecious life cycle shown by the black bean aphid, Aphis fabae, and the peach-potato aphid, Myzus persicae (Figure 3.1), in which there is a wide range of secondary host plants, is very rare. Even in these highly polyphagous species it is possible that particular genotypes do best on certain species of plant (Takada, 1979; Weber, 1985a-c), i.e. most aphids show a very high degree of host specificity, even the heteroecious species.