The growth and decline of a population of the spruce aphid Elatobium abietinum during a three year study, and the changing pattern of fecundity, recruitment and alary polymorphism in a Northern Ireland Forest.

The population size and structure of the green spruce aphid was followed throughout the spring - summer cycle on the same group of trees in a low-elevation coastal Sitka spruce forest for three consecutive years. The relationship between the pattern of change and the phenology of bud burst, which heralds a marked change in needle sap quality, suggests that yearly differences in the winter temperature regime may affect the duration of the population growth phase and hence the peak numbers attained in late spring.An index of population growth rate was sufficiently sensitive to aphid fecundity during the population cycles of two years to suggest that the changing rate of fertility was the decisive process governing changes in population size. The commitment of aphids to alate development was greater than that recorded elsewhere in Britain but did little to effect population decline since the contribution of alatae to larviposition was substantial while seasonally pulsed.