AN INVESTIGATION OF THE DIFFERENTIAL PERFORMANCE OF CLONES OF THE APHID SITOBION-AVENAE ON 2 HOST SPECIES

Individuals of the grain aphid Sitobion avenae were collected from whe at and cocksfoot stands around Hampshire, UK, during March and April 1 994. Eight wheat and eight cocksfoot aphid clones were chosen on the b asis of readily distinguishable RAPD-PCR fingerprint profiles. The per formances (weight, fecundity and survival) of successive generations o f each of these clones were then carefully monitored in the laboratory as new generations of aphids were transferred either to winter wheat or to cocksfoot in planned sequences. Even those clones that were orig inally caught on the same host showed significant variability in perfo rmance. Clones generally performed better on their host of origin than they did on the alternate host, and they performed less well on the a lternate host compared to the clones that had originated there. A comp arison of the performance of third generation aphids with first genera tion aphids showed that the experience of the mother in the second gen eration often influences the subsequent performance of their offspring . As the sequence of host transfers had more effect on the performance of wheat clones than cocksfoot clones, it is likely that wheat clones are more specialised, such that wheat is a satisfactory host for cock sfoot clones but not vice versa. The study provides evidence of geneti c variation in performance on hosts and evidence for clonal adaptation to particular host species. This adaptation may well be a major cause of the observed consistent genetic differentiability of populations o f S. avenae found on wheat and roadside grasses in early spring in sou thern England.