The role of aphids in wood formation. I. The effect of the sycamore aphid, Drepanosiphum platanoides (Schr.) (Aphididae), on the growth of sycamore, Acer pseudoplatanus (L.).
The following is virtually the author's summary of this account of observations in Scotland [cf. RAE A 54 678; 59 1153, 2160]. A sycamore tree kept under observation during 1961-68 produced small leaves when heavily infested by Drepanosiphum platanoides (Schr.) in spring. Although the leaf size is related to the available nutrient supply, the aphids caused a reduction in leaf size far greater than would be expected from the quantity of nutrients removed by them. In years when the aphids. are abundant in the spring, the leaves fall still rich in nitrogen in autumn. The annual ring laid down in the trunk of the tree was found to be related to the size of the leaves and the number of aphids present on the tree through the year. In the absence of aphids, sycamore trees could produce as much as 280% more stem wood. Experiments on saplings under controlled conditions showed that aphid infestation can regulate leaf size, growth and the quantity of nitrogen in the leaves at leaf fall. Leaves infested with aphids had a net dry-matter production-rate 1.7 times greater than uninfested leaves. Aphid infestation in the previous year did not affect the size of the leaves in the current year, but the leaves were paler in colour than those of previously uninfested saplings. The size of the annual ring was related to the leaf area it supplied. However, a smaller annual ring was laid down round existing annual rings than in twigs of the current year. Tree growth and the way in which aphids affect it are discussed.