I. SOME PATTERNS

SUMMARY (1) Over half a million individuals were counted in eight populations of the sycamore aphid over a 9-year period. (2) The changes in spring and autumn numbers from year to year indicated that all eight populations were subject to density-dependent regulation and that the populations displayed a range of dynamic behaviour. All populations persisted throughout the study. (3) Comparison of population growth rates revealed that populations in any one year were often in synchrony. This reflects the important role of weather in driving aphid numbers. (4) During the summer, second generation adults aestivate. Analysis of reproductive rates of caged individuals revealed that the duration of this aestivation was densitydependent, but undercompensatory. (5) The synchrony of the sexual morphs in autumn was dependent on recruitment during July and thus linked with the duration of aestivation. (6) Analysis of field data revealed some associations between the aphid and its host plant. The time of leaf fall was correlated with autumn aphid densities, and the time of bud break and egg hatch related to the aphid densities in the previous autumn.