SPATIAL AND TEMPORAL GENETIC-VARIATION IN BRITISH FIELD POPULATIONS OF THE GRAIN APHID SITOBION-AVENAE (F) (HEMIPTERA, APHIDIDAE) STUDIED USING RAPD-PCR

The grain aphid Sitobion avenae (F.) was collected from winter wheat a nd adjacent cocksfoot grass at two locations in southern England and a t four times in the year (April-July). Genetic variation between indiv idual aphids was then investigated using random amplified polymorphic DNA polymerase chain reaction. Individuals caught in wheat and cocksfo ot during April provided very different and highly diagnostic banding patterns that were independent of location. This host-based genetic di fferentiability was less evident as the season progressed, largely as a result of genetic drift and local movement between adjacent host spe cies, which appeared to be predominately in the direction from cocksfo ot to wheat. The diversity of putative clones fell significantly, the mean number of individuals per clone rose and clones became more exclu sively associated with certain sites which suggests that long-distance migration may have less of a homogenizing effect than hitherto though t for this species.