On aphids, their host plants and speciation : a biosystematic study of the genus Cryptomyzus

Allozyme data as determined by starch gel electrophoresis revealed that all species of Cryptomyzus could be distinguished on the basis of unique alleles. Moreover, differences were detected between the two forms of C.alboapicalis, which do not host-alternate and instead live on Lamium album and L. maculatum , respectively. In the C. galeopsidis complex as well a form that host-alternates between Ribes rubrum and L. galeobdolon was distinguished. The two non- alternating subspecies on R. rubrum and R.nigrum, respectively, differed in allozyme frequency, indicating a reduced gene flow. Electrophoresis proved a powerful tool in unraveling relationships of closely related aphid complexes (Chapter 1).The life cycle of C.heinzei was elucidated by the discovery that Ribes alpinum is the winter host and Stachys officinalis the summer host. No populations survived on the originally described summer host plant of this species, Satureja vulgaris , probably indicating that the host plant was initially misidentified. In laboratory experiments R. alpinum appeared to be the winter host of C.ballotae although reproduction and developmerit on this plant were weak. A full account of the host plants of Cryptomyzus species is given in Chapter 2.Closely related forms of C. alboapicalis and C.galeopsidis revealed a definite host plant preference for their own particular summer host plant. This fact was corroborated by the host plant suitability, based on the reproductive performance of these forms. Significantly, for the development of reproductive isolation those morphs returning to the winter host exhibit a prefererence for the host on which their stem mother was born. Experiments confirmed this feature in the case of host- alternating clones of C.galeopsidis from R. nigrum, although host preference of those from R. rubrum proved to be ambiguous. Several clones preferred R. rubrum on which their oviparae matured, while others preferred R.nigrum on which their oviparae matured as well.