The invasive plant Lonicera maackii (Amur honeysuckle) has had a variety of ecological effects as it continues to spread through the eastern United States including the loss of plant biodiversity and alterations in ecosystem function in forests. Streams meander through many forests where Amur honeysuckle is present and recent evidence suggests that this terrestrial invasion has consequences for stream biology. Leaves of Amur honeysuckle have been shown to have strong negative effects on terrestrial insects and we hypothesized that these negative effects may also occur in aquatic macroinvertebrates. In this set of experiments we used a sequence of microcosm assays to assess the influence of Amur honeysuckle leachate on the macroinvertebrate Hyalella azteca, which is a standard “model” aquatic organism to toxicity assessment In the lab, H. azteca were exposed to riparian honeysuckle leaf leachate (made by soaking 10 g leaves in 100 mL dechlorinated water for 24 h) in 48 h acute, static toxicity tests. This was repeated throughout the growing season. When exposed to an Amur honeysuckle leachate dilution series (6.25%, 12.5%, 25%, 50%, 100%), H. azteca survival was significantly decreased in all dilutions in the spring and fall trials. However, the summer trials showed no significant decrease in survival in nearly all the dilutions. These results suggest (a) strong toxic effects of Amur honeysuckle foliage on a model aquatic organism that (b) varies throughout the year, potentially in relationship to biochemical changes associated with phenology. Future experiments regarding the chemical composition and toxicity of these leaves should be mindful of the season in which the leaves are gathered. This study supports the importance of management of Amur honeysuckle in headwater stream riparian zones which are particularly vulnerable to perturbations and are increasingly a focus of conservation
