Submitted to: XI Symposium on Biological Control of Weeds
Publication Type: Proceedings
Publication Acceptance Date: 11/20/2003
Publication Date: 7/20/2004
Citation: Proceedings of the XI International Symposium on biological Control of Weeds. CSIRO Entomology, Canberra, Australia pp 180-185
Interpretive Summary: Alligator weed, Alternanthera philoxeroides (Mart.) Griseb, is an herbaceous amphibious weed of the Amaranthaceae, native to southern South America. Several agents from Argentina, Agasicles hygrophila Selman and Vogt and Arcola malloi (Pastrana) have been used successfully for the biological control of the water-growing alligator weed in Australia and USA. In Australia, the weed continues to pose a serious problem particularly in terrestrial situations. 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. In Argentina, alligator weed 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 (Martius) Grisebach f. philoxeroides (Mart.) Griseb. in the southern range and A. philoxeroides (Mart.) Griseb. angustifolia Süssenguth in the northern range. Both are distinguished by leaf and inflorescence shape and stem diameter. There also appears to be preferential attack by flea beetles on A. p. angustifolia. After the initial year of surveys, the natural enemies that may have biological control potential include: two species of leaf feeding beetles, Systena spp.; a tip galling Cecidomyiidae fly; two agromyzid flies, one that causes node galls and another that mines leaves. Several pathogens were also found; one probably Nimbya alternantherae, known to have a wide host range, and another, thought to be Sphaceloma new species, that causes a characteristic 'corky' deformation on the stem and leaf surfaces. Further studies will extend the surveys and also aim to assess the interactions between these herbivores and pathogens with alligator weed and to obtain preliminary host range information.
Technical Abstract: The SABCL has been conducting surveys searching for new biological agents of the amphibian weed alligator weed, Alternanthera philoxeroides (Martius) Grisebach (Amaranthaceae). We found two distinctive forms of the plant, both of them easily recognizable by the leaf shape, flowers and stems (narrow or broad). They were identified as A. philoxeroides philoxeroides (Mart.) Griseb. and A. philoxeroides angustifolia S'ssenguth. We found A. philoxeroides philoxeroides in the south of the native range of the weed, whereas the other form in the northern range. In spite of the known biological suppressants of the weed- such as Agasicles hygrophila, Amynothrips andersoni, Arcola malloi and Disonycha argentinensis-we found other insects. They are: flea beetles in the genus Systena, a tip galling fly in the Cecidomyiidae, two agromyzid flies (one causes leaf mines and the other makes galls in the stem nodes). Furthermore, pathogens were also found, one of them is a known pathogen on this plant, Nymbia alternantherae. Other pathogens were found producing a deformation of the stems and leaves making them a corky appearance, it is apparently one species of Sphaceloma. We expect to conduct more surveys to obtain an accurate study of the association of these possible agents and alligator weed.