An Investigation of Herbivory on the Invasive Grass Phragmites australis subspecies australis Lydia Truitt and Cynthia Kicklighter Goucher College, Baltimore, MD Introduction Tracking Down the Deterrent Chemical: Results The ingress of invasive species often results in ecological damage and reduced biological diversity. The Eurasian marsh grass Phragmites australis subspecies australis is one of Maryland’s most successful invaders in both terrestrial and wetland areas. Previous research has determined that Phragmites uses a chemical defense to deter snail herbivory by decreasing palatability, but it is unknown how Phragmites may defend itself from other herbivores. Choice feeding bioassays were used to investigate the effectiveness of Phragmites’ structural and chemical defenses for an array of herbivores, including the Periwinkle Snail (Littoraria irrorata), Dusky Slug (Arion subfuscus), and Mealy Plum Aphid (Hyalopterus pruni). In addition, because herbivore grazing can increase the production of plant defenses; we grew Phragmites in the absence or presence of snails. The use of chemical separation techniques continues in an effort to identify the responsible chemical(s) used by Phragmites to deter snail herbivory. Dusky Slug (Arion subfuscus) Periwinkle Snail (Littoraria irrorata) Mealy Plum Aphid (Hyalopterus pruni) Is Phragmites Eaten? Research Question How does Phragmites fit into the local food web? Wetland Herbivores: Terrestrial Herbivores: 1. Mealy Plum Aphid 2. Periwinkle Snail 1. Mealy Plum Aphid 2. Dusky Slug Above: Slug choice feeding bioassay between whole romaine lettuce and Phragmites leaves Above: Snail choice feeding bioassay between ground Ulva and ground Phragmites Above: Aphid choice feeding bioassay between Spartina and Phragmites Left: Slug in bioassay between romaine lettuce and Phragmites Above: Bioassay guided fractionation flowchart for tracking down the deterrent chemical Below: High performance liquid chromatography spectrogram of the 55:45 water:methanol deterrent fraction Why Not? Phragmites Defense Structural? Conclusions Chemical? Induced Response? Methods Above: Slug choice feeding assay between ground lettuce and ground Phragmites Above: Snail choice feeding assay between Ulva & Ulva with Phragmites chemical extract. Left: Completed slug feeding assay between ground romaine lettuce and Phragmites Right: Snails in choice feeding assay Induced Chemical Defense? A B • Neither the slug nor the aphid were deterred by Phragmites’ chemical defense • The slug was deterred by Phragmites’ structure • Snails were deterred more by Phragmites that had been previously fed on by snails compared to ungrazed Phragmites • Aphids fed on grazed versus ungrazed Phragmites equally • Our results suggest that native herbivores find Phragmites less palatable than do non-native herbivores • The deterrent chemical is moderately polar but is yet to be identified Acknowledgements C D Above: A Setting up feeding assay strips B Slugs in feeding assay C Extracting chemicals from Phragmites. D Putting up 0.08m2 snail inclusion/exclusion cages at the field site Above: Snail choice feeding assay between Phragmites grown in the presence and absence of snails Above: Aphid choice feeding assay between Phragmites grown in the presence and absence of snails Left: 0.08m2 caged plots Right: Aphids in feeding assay between Phragmites grown with or without snails Ashley Privett Hannah Locke Lindsay Hendricks Andrew Mellon Foundation Goucher Summer Research Program Chesapeake Bay Environmental Center