Apparent widespread gene flow in the predominantly flightless planthopper Tumidagena minuta

1. To determine whether dispersal biology can predict the pattern of popula tion-genetic variation among insect populations accurately, allozyme variat ion was assayed for populations of a saltmarsh planthopper, Tumidagena minu ta, in which >99% of the adults are flightless. 2. The pattern of genetic i solation by distance in T. minuta was compared with that in other insects, to determine whether it was similar to isolation by distance in other seden tary insects. 3. In contrast to predictions, the pattern of isolation by di stance in T. minuta was most similar to that seen in the most mobile insect s in a recent review of population-genetic subdivision over a genetic varia tion in insects. Furthermore, population spatial scale of >400 km was weak. 4. Possible causes of the apparent contradiction between dispersal biology and population-genetic structure in this species are discussed. The result s for T. minuta highlight the fact that although mobility is generally corr elated with gene flow in insects, studies of population-genetic variation m ust be combined with direct studies of dispersal to understand fully the de gree to which populations exchange individuals.