GEOGRAPHIC AND MICROGEOGRAPHIC GENETIC DIFFERENTIATION IN 2 APHID SPECIES OVER SOUTHERN ENGLAND USING THE MULTILOCUS (GATA)(4) PROBE

Samples of the grain aphid Sitobion avenae (F.) and the rose-grain aph id Metopolophium dirhodum (Walker) were collected in late March from w heat fields and adjacent road-side grasses at a number of locations in southern England. Unparasitized aphids were DNA fingerprinted using t he multilocus (GATA)(4) probe. Over all locations, the fingerprints of individual S. a avenae caught in wheat had lower overall average dist ances of band migration (ADBM) and shared a higher proportion of bands , than fingerprints of individuals caught in adjacent road-side grasse s. The ADBM of fingerprints of S. avenae collected on road-side grasse s altered significantly with geographical location, while the ADBM of fingerprints of S. avenae caught on wheat did not. A comparison of the fingerprints of individual M. dirhodum caught in wheat and neighbouri ng road-side grasses did not reveal any genetic differentiation. Finge rprints of M. dirhodum that were caught in the same host type did howe ver, show significant variation in ADBM between different locations. W ith both S. avenae and M. dirhodum, spatial autocorrelation revealed t hat locations that were close together were no more likely to have ind ividuals with similar ADBM than locations that were far apart. Our res ults suggest that (i) particular clones of S. avenae prefer to coloniz e wheat, and/or that (ii) particular clones of S. avenae perform bette r on wheat than other clones. It is unclear why M. dirhodum did not sh ow any genetic structuring according to host type, but this species ap pears to engage in sexual reproduction much more frequently than S. av enae in southern England. M. dirhodum is likely td have displayed gene tic heterogeneity between locations either because of founder effects, or because of genetic drift.