Abstract
The effect of shoot growth of Spiraea thunbergii on colonization of Aphis spiraecola was investigated in the field. Shoot length of S. thunbergii increased from early April to mid-July and the number of A. spiraecola peaked in early May. The aphids tended to colonize better growth shoots rather than the lesser ones, although the shoot growth was damaged by the aphid infestation. The maximum aphid density (no. of aphids/mm per shoot) for all the shoots was constant regardless of shoot length, suggesting that aphid dispersal is density-dependent.
