Genotypic variation and structure in Australian populations of the aphid Schoutedenia lutea

The genotypic variation and genetic structure of populations of the aphid Schoutedenia lutea were investigated in the Sydney area of Australia. The typical growth curve of an aphid population was observed: exponential increase in spring (September‐October), highest density in the summer (early January), and a collapse by autumn (early March). During the growth period, the frequency of alatae decreases, but the frequency of sexual morphs (oviparae, males) is fairly constant. Three enzyme markers were used to study genotypic variation. Only 11 out of 27 possible genotypes were found, There was no change in genotype frequencies throughout the growth period. To investigate the genetic population structure, aphids were sampled from twigs within and among bushes of Breynia oblongifolia from two ecologically different areas (Cumberland State Forest, Pearl Beach). Analysis of heterogeneity revealed that genetic variation on the host plants of aphids contributes as much as 61 % to the total heterogeneity, whereas the effect of areas was 23 %. The results are discussed with respect to life cycle components and migration of the aphid, and are compared with results from Macrosiphum rosae in Europe.