Population dynamics of a tree-dwelling aphid: individuals to populations

The model presented simulates most of the observed features of the population dynamics of tree-dwelling aphids: a sharp increase in numbers during the first 15–40 days, followed by a sharp decline to a plateau of low numbers in summer and a recovery in autumn, in some years. The larger the numbers at the beginning of the season, the larger and earlier the peak. Migration is shown to be the most important factor determining the summer decline in abundance, while changes in aphid size and food quality account for why the autumnal increase is less steep than in spring. Finally, the model suggests a possibility of a “see-saw effect” (a negative correlation between spring and autumn peak numbers) in some cases.