Growth-chamber experiments were conducted to assess the relationship between initial colony size and the subsequent growth and alate production of the Russian wheat aphid, Diuraphis noxia, feeding on winter wheat. Per capita growth of aphid colonies declined slightly as initial density increased, but was largely insensitive to the degree of crowding (with mean final densities up to ca. 1000 individuals/tillering plant). I detected no evidence of optimal growth at intermediate densities, which would have been expected if aphid aggregation caused a beneficial modification of the common feeding site. Alate production was positively related to the density of the aphid colony, but density explained only 15-35% of the variation in the percentage of alates. Much of the unexplained variation in alate production was due to uncontrolled maternal effects; results of an experiment in which all 'founding' aphids developed under uncrowded conditions suggested that prenatal conditions overwhelm post-natal effects on the wing polymorphism in parthenogenetic generations of D. noxia.