New research on Alternanthera philoxeroides (alligator weed) in its South American native range

A.J. SOSA; M.H. JULIEN; H.A. CORDO

Simposio; XI International Symposium on Biological Control of Weeds; 2003

Alternanthera philoxeroides (alligator weed) is a herbaceous amphibious weed of the Amaranthaceae, native to southern South America. Several agents from Argentina, e.g. Agasicles hygrophila and Arcola malloi, have been used to control aquatic A. philoxeroides in Australia and the USA. However, in Australia, the weed continues to pose a serious problem, particularly in terrestrial situations. In Argentina, A. philoxeroides is distributed along the catchments of the Paraná and Uruguay rivers in the north, and in the catchments of the San Borombón and Salado rivers in the centre of Buenos Aires province. Two forms are recognized: A. philoxeroides f. philoxeroides in the southern range and A. philoxeroides f. angustifolia in the northern range. There appears to be preferential attack by flea beetles on A. philoxeroides f. angustifolia. In 2000, the CSIRO initiated a collaborative research project with the USDA South American Biological Control Laboratory in Argentina to search for new biological agents. After the initial year of surveys, the natural enemies that may have biological control potential included: two species of leaf-feeding beetles, Systena spp.; a tip-galling Cecidomyiidae fly; and two agromyzid flies, one that causes node galls and another that mines leaves. Two fungi were also found: one probably Nimbya alternantherae, known to have a wide host range, and another, thought to be a new Sphaceloma species, that causes a characteristic “corky” deformation on the stem and leafsurfaces. Surveys will be extended and the interactions between these herbivores and  pathogens with A. philoxeroides will be studied.