Phragmites australis invasion alters the structure and function of diverse marsh ecosystems by changing species composition, nutrient cycles and hydrological regimes. Dense Phragmites stands in North America decrease native biodiversity and quality of wetland habitat, particularly for migrating waders and waterfowl species.
Research in North America and Europe began in 1998 with literature and field surveys for potential control agents (Tewksbury et al., 2002). As of 2002, no deliberate introductions of biological control agents have occurred. However, currently (2002) 26 herbivores are known to attack P. australis in North America. Many of these species were accidentally introduced during the last decades; only five are potentially native (Tewksbury et al. 2002). The diversity of accidentally introduced Phragmites herbivores is highest closest to New York City. This suggests that a major source for the introduction of arthropods is transcontinental shipping. Various introduced species associated with Phragmites appear to be spreading from New York City along highways, rivers, and the coastline. Many introduced species such as several shoot flies in the genus Lipara, a rhizome feeding noctuid moth Rhizedra lutosa, the gall midge Lasioptera hungarica, a dolichopodid in the genus Thrypticus, the aphid Hyalopterus pruni, and the wasp Tetramesa phragmitis, appear widespread. The mite Steneotarsonemus phragmitidis was recently discovered in the Finger Lakes Region of New York and the rice grain gall midge Giraudiella inclusa in Massachusetts, Connecticut, New Jersey, and New York.
In Europe, at least 140 herbivore species have been reported feeding on P. australis, some causing significant damage (Tewksbury et al. 2000). About 50% of these species are considered Phragmites specialists and almost 40% of the species are monophagous (feed only on P. australis). Lepidoptera (45 species) and Diptera (55) are the most important orders. Over 70% of all these herbivores attack leaves and stems of P. australis, and only 5 of the monophagous species feed in rhizomes. Of the 151 Phragmites herbivores known from outside North America, already 21 (13.9%) have been accidentally introduced.
Work in Europe and North America will continue simultaneously to assess the potential of accidentally introduced herbivores and those restricted to the European range as biological control agents. Promising biological control agents have been identified in Europe and their impact and host specificity needs to be determined experimentally.