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Peer-Reviewed Article

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Eurasian watermilfoil (Myriophyllum spicatum) is often considered one of the most aggressive macrophyte invaders in freshwater habitats throughout the United States. However, conditions leading to successful milfoil invasions are not well understood. This study sought to illuminate the role of 4 herbivores in determining milfoil invasion success via either enemy release or biotic resistance. We determined feeding preferences of three herbivores native to the northeastern United States and measured milfoil phenolic content, which may act as an herbivore feeding deterrent. We found that phenolic content in milfoil was two times higher than in two of the most abundant native macrophytes at our study sites, consistent with enemy release. However, laboratory feeding experiments demonstrated that milfoil phenolics did not deter amphipod (Hyalella azteca), snail (Physella sp.), or weevil (Euhrychiopsis lecontei) herbivory, contrary to the predictions of enemy release. Amphipods and snails from habitats invaded by milfoil consumed similar quantities of both milfoil and the low-phenolic native plant Elodea canadensis. In contrast, weevils consumed milfoil but not E. canadensis. Amphipods collected from milfoil-free habitats also readily consumed milfoil, and they consumed two to three times more milfoil than E. canadensis in choice feeding trials. These results suggest that high phenolic levels do not prevent native herbivores from consuming invasive milfoil. Instead, native generalist grazers like amphipods and snails may limit milfoil proliferation and provide a measure of biotic resistance.


This work was funded by a Sacred Heart University Research and Creativity Grant to LaTina Steele and a United States Geological Survey 104B Grant via the Connecticut Institute of Water Resources awarded to LaTina Steele and Michele Guidone (primary award #G11AP20069, subaward #59773).

This links to the author's personal copy of an article that has been published in the journal Aquatic Ecology. Link to the definitive version on the publisher’s website:





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