The tale of two invaders: the common reed and the mealy plum aphid

Common reed (Phragmates australis) has been conquering the salt and brackish marches of the East coast for over half a century. The plant form extensive stands densely covering all available marsh surface and leaving little room for anything else. Scientists discovered that the aggressive form of the common reed is actually an exotic plant introduced from Europe but closely related and almost indistinguishable from the native North American version. The European type outcompetes the native plant, partially due to another invasive passenger it brought along from the old country: Mealy Plum Aphid (Hyalopterus pruni).

 This little aphid sucks the plant juices causing leaf damage. When the aphid numbers are low, the injury is hardly visible.

However, when the aphid populations go up, the damage (such as leaf browning seen here) becomes more obvious. The problem is that mealy plum aphids prefer the native common reed over the introduced form, and reach much higher numbers on the native plants capable of killing them outright. The exotic invasive form of common reed is not as attractive harboring the aphids without extensive injury to the plant. This insect might be contributing to the invasive form takeover of the marshes by selectively weakening or destroying the native plants.

 Mealy plum aphids have two color types, green and red. The significance of this is unknown. 

Source: Lambert AM, Casagrande RA. Susceptibility of native and non-native common reed
to the non-native mealy plum aphid (Homoptera: Aphididae) in North America.
Environmental Entomology 36(2):451-7.