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  • Author or Editor: Z. Basky x
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The common ragweed, Ambrosia artemisiifolia (L.), is a widespread invasive weed species in Europe. In order to estimate the hampering effect of native arthropods on the invasive ragweed, the effect of three indigenous aphid species on plant development and pollen production was studied. Common ragweed plants grown in a greenhouse were artificially infested with five apterous individuals of either Aphis fabae Scopoli, Brachycaudus helichrysi (Kaltenbach) or Myzus persicae (Sulzer) at the 4-leaf stage. Feeding by all three aphid species over a five-week period significantly reduced plant height, the number of male inflorescences, the length of racemes, pollen emission and plant dry weight. Brachycaudus helichrysi produced the largest colonies, followed by A. fabae and M. persicae. In a field experiment, the growth rate of A. fabae on caged ragweed plants was similar to that in the greenhouse, but the final numbers of B. helichrysi and M. persicae after 30 days was ten and seven times lower, respectively than under greenhouse conditions. On exposed field plants, B. helichrysi was significantly more abundant than the other two species. However, no aphid species affected the height or dry weight of either caged or exposed plants during a 30 days period. However, during longer exposure (83 and 112 days) the exposed plants suffered more from aphid feeding and this resulted in significant plant height and dry weight decrease regardless of the aphid species. However, statistical significance is not necessarily equivalent to biological significance. Naturally occurring aphids can enhance the ability of native vegetation to counter the weed but their effect is not strong enough on its own to drive down the number of this invasive species.

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