The biology of some host-adapted populations of A. gossypii and the comigration band mobilities of aphid enzyme extracts were studied in 1992 in Kochi, Japan. Results indicated that biologically there are no significant differences between eggplant, cucumber and watermelon aphid populations with regards to longevity and the number of offspring produced per female aphid. However, in all populations, adult survival declined significantly within 5 days of introduction onto a new host from the original. No genetic differences were observed between populations since they scored equally at seven different enzyme loci: malic enzyme (ME), glucosephosphate isomerase (GPI), isocitrate dehydrogenase (1DH), phosphoglucomutase (PGM), 6-phosphogluconate dehydrogenase (6-PGD), malate dehydrogenase (MDH) and naphthylacetate linked esterase (EST). Also, protein bands, as revealed by SDS-PAGE, as well as carboxylesterase banding patterns, showed no differences between populations. These results indicate that the various host-adapted populations of A. gossypii infesting a wide range of solanaceous and curcubitaceous crops can be treated as single species devoid of genetic variability. The slight differences in biology and behaviour found between the various hostadapted populations can be attributed to physiological variations, differences in host nutrient composition, and possibly to some unknown co-existing biotic factors.