Invasions of exotic plants constitute a major threat to aquatic ecosystems. West Indian Marsh Grass, Hymenachne amplexicaulis (Rudge) Nees, is currently invading the watersheds of central and south Florida. During the fall of 2000 H. amplexicaulis showed severe damage caused by an unknown blissid, which was later identified as Ischnodemus variegatus, a new record for United States. The potential of this herbivore to control H. amplexicaulis and its host range were evaluated under laboratory and greenhouse conditions. Ischnodemus variegatus infestations were capable of reducing the growth rate, chlorophyll levels and biomass of H. amplexicaulis. Early damage of I. variegatus on seedlings of H. amplexicaulis was characterized as brown rounded necrotic spots on the leaf. If the infestation continues, some parts of the leaf turn red. So far, non-choice tests demonstrate that I. variegatus nymphs complete development only on H. amplexicaulis. Detailed analysis of the I. variegatus impact on plant performance mediated by soil moisture and its potential as biological control agent are discussed.