POPULATION GENETIC-STRUCTURE DURING ESTIVATION IN THE SYCAMORE APHID DREPANOSIPHUM-PLATANOIDIS (HEMIPTERA, DREPANOSIPHIDAE)

Cellulose acetate electrophoresis was used to investigate genetic vari ation at 15 enzyme loci in aestivating populations of the sycamore aph id, Drepanosiphum platanoidis (Schrank) (Hemiptera: Drepanosiphidae). The level of polymorphism P (over all loci) was 20%. Of the polymorphi c loci, only phosphoglucomutase (PGM), with four alleles, provided con sistent, interpretable banding patterns and was subsequently used to i nvestigate population structure and gene flow at various spatial level s in southern Britain. Of 13 aphid aggregations (from single leaves) c ollected from the lower canopy of a selected tree, only one deviated s ignificantly from Hardy-Weinberg expectations. Genotypic diversity for the PGM locus was generally high and genetic identity measures showed homogeneity between leaf aggregations. Aphid samples collected from e ight trees in close proximity, five sites in Hertfordshire and four ot her sites in southern Britain, also showed homogeneity for alele and g enotype frequencies and, in almost all cases, conformed to Hardy-Weinb erg expectations. It was concluded that gene flow, facilitated by triv ial and migratory flight, was responsible for the genetic homogeneity observed, both within and between host trees.