A reappraisal of flight regulation in the green spruce aphid, Elatobium abietinum

SUMMARY Alate formation and its importance in the population dynamics of Elatobium abietinum is examined. It is concluded that alate formation is related to high soluble nitrogen levels in Sitka spruce needles. In N.E. Scotland the proportion of the population developing as alatae was related to aphid density. The apparently differing status of alatae in S. England may be related to differences in the physiology of the host caused by heat input. In Scotland alate formation may cause a decline in spruce aphid populations when densities are very high but, at the densities normally encountered in Scotland and Germany only small proportions of the populations become alate. In these areas the population collapses in late June or early July occur in response to low soluble nitrogen levels in the spruce needles. The role of alate adults in the formation of new colonies following migration to uncolonised hosts is discussed.