The population dynamics of the large pine aphid,Cinara pinea (Mordv.)

Summary

The paper describes the development of a computer model designed to simulate the field population dynamics of the large pine aphid,Cinara pinea. Emphasis was placed on the analysis of intrinsic factors influencing population changes and no attempt was made to include natural enemy functions at this stage. The model was able to account for 52% of the numerical variation within and between experimentally controlled populations on saplings in the field. Agreement between the model’s predictions and population dynamics on mature field trees was also good, particularly during the early part of the season. Only after the midsummer peak do significant discrepancies emerge, the difference reflecting the likely impact of natural enemies, which became abundant at this time.

Intrinsic density-dependent processes, while shown to occur inCinara pinea, were found to be of little significance in determining population numbers in the field. In practice, it is seasonal and between-tree variations in plant quality that appear to be of major importance in determining population densities in the field. Predators, too, by influencing numbers later in the season are likely to affect the number of overwintering eggs laid and hence the peak number the following year. However, even in the absence of predation, tree quality effects are capable of restricting aphid numbers to within field-observed limits over a period of years.