The effects of nutrition and density on the production of alate Elatobium abietinum on Sitka spruce.

Observations over a period of 10 years showed that, in Northeastern Scotland, alatae of E. abietinum regularly appeared in mid-May, the timing being unrelated to aphid density. The peak number of alatae produced was, however, correlated with aphid density. Following an initially high level the proportion of alatae dropped to virtually nil by mid-June, whilst over the same period the aphid population density increased. Amino acid levels in spruce needles were considerably higher during the period of alate formation than they were at the termination of alate production. It is suggested that a high amino acid level was the main factor controlling the formation of alatae and that population density affected the proportions of these alatae only when nutritional levels were favourable for alate formation.