Bayreuther Institut für Terrestrische Ökosystemforschung
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Stadler, B; Müller, T: Aphid honeydew and its effect on the phyllosphere microflora of Picea abies (L.) Karst., Oecologia, 108, 771-776 (1996)
Aphids of the genus Cinara, feeding on Norway spruce, excrete copious amounts of honeydew, a carbon rich waste product, which locally accumulates on needles and twigs. We investigated the role of honeydew as a potential source of energy, which might promote the growth of microorganisms in the phyllosphere of conifer trees. To approach this question we followed the population dynamics of Cinara spp. in a natural forest stand during two seasons. We further studied the amounts of honeydew produced by individual aphids and identified potential parameters which might influence honeydew production. Finally, we determined the growth of microorganisms on infested and uninfested needles of Norway spruce during the growing season. While confined to Picea abies the investigated Cinara species only became abundant in midsummer, when needles and shoots were expanding. The populations showed only a single peak in abundance, the timing and the magnitude of which may vary from year to year due to weather conditions, changes in plant quality in a yearly cycle or due to the impact of natural enemies. The amount of honeydew produced by individual aphids was dependent on the developmental stage of the aphid, the nutritional supply of its host plant and to the developmental state of Norway spruce (e.g. bud burst, end of shoot extension). The presence of honeydew significantly increased the growth of bacteria, yeast and filamentous fungi on the surface of needles and there is a pronounced seasonal trend with highest abundance in midsummer correlating with the period of peak abundance in aphids. We integrate these findings and pronounce the role of aphids influencing the microbial ecology in the phyllosphere of trees. The implication of our study, including interactions at the population level to effects and potential consequences for C and N-fluxes at the level of forest ecosystems, is discussed.
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