Local population dynamics of two co-existing birch aphid species : competition or intrinsic cycles of abundance? (original) (raw)
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2013
Achillea collina Becker ex Rchb. (yarrow) is a medicinal plant grown for commercial purposes in southern Switzerland and northern Italy. The economically most relevant population assemblage is organized around the phloem feeding aphids Macrosiphoniella millefolii (De Geer), Aphis spiraecola Patch and Coloradoa achilleae Hille Ris Lambers. The study is a contribution to explaining the dynamics of this assemblage in two Alpine fields, on the basis of multitrophic population interactions. The method consisted in stratifying the field and taking random samples of yarrow stems and leaves, aphid numbers, and numbers of adult coccinellids and mummified aphids throughout the growing period. There were no significant differences in aphid densities between the strata (α = 0.05; F = 1.561; P = 0.138). Once the photoperiod reaches 14 h, a time window opens for stem elongation and reproductive development that creates suitable conditions for the aphids. There are indications for an influence of ...