Colonization Patterns of Aulacorthum magnolidae (Aphididae : Homoptera) on Sambucus sieboldiana (Caprifoliaceae); the Impact of Predatory Disturbance on an Aphid Colony and the Effects of Aphid Colonization on Plant Structure

Colonization patterns of Aulacorthum magnolidae on Sambucus sieboldiana were investigated. The relationship between the maximum shoot length and the maximum aphid number was not significant, while there was a significantly negative correlation between shoot length and the maximum aphid density. These results suggest that a density-dependent process did not operate in A. magnolidae colonization. In total, 98.68% of the shoots examined were colonized by the aphids and 53.95% died. The survived shoots were longer at the initial aphid colonization than those which died, and furthermore the basal shoots of a twig rarely died, indicating that the timing of the initial aphid colonization and the shoot's location on a twig were important in determining death or survival of the shoots. Field observations and an artificial predator introduction experiment indicated that predatory disturbance may be one of the most important factors which promote aphid movement between shoots.