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