THE ROLE OF FOOD QUALITY AND COMPETITION IN SHAPING THE SEASONAL CYCLE IN THE REPRODUCTIVE ACTIVITY OF THE SYCAMORE APHID

The hypothesis that seasonal changes in sycamore aphid, Drepanosiphum platanoidis (Schr.), recruitment are determined by changes in food qua lity and aphid population density was tested. There was no clear assoc iation between the reproductive activity of the sycamore aphid and the seasonal changes in specific amino acids or groups of amino acids in extracts of sycamore, Acer pseudoplatanus L., leaves. Seasonal changes in reproductive activity tracked the changes in total amino acids of the leaf tissue of the host, but with a short time delay. High numbers of adult aphids appeared to depress reproductive activity. A regressi on analysis of the results revealed that total amino acids the previou s week and current numbers of adult aphids significantly affected syca more aphid reproductive activity. The results of this analysis support the above hypothesis, that the marked seasonal changes in the total q uantity of amino acids in sycamore leaves and intraspecific competitio n for this resource, through its effect on adult weight, shape the sea sonal cycle in the reproductive activity of the sycamore aphid.