The biological control of alligatorweed, Alternanthera philoxeroides, in the United States of America

Abstract

Alligatorweed, Alternanthera philoxeroides (Mart.) Griseb., an aquatic amaranth introduced into the United States from South America around 1900, was recognized as a threat to the aquatic ecosystem as early as 1901. It has been classed as a weed because of its competitive advantage over our native flora. A 1963 survey found the weed commonly throughout the southeastern United States. Alligatorweed was estimated to infest 65,700 ha in the states of North and South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas. Biological control of alligatorweed was begun in 1960 with surveys in South America for natural enemies. Research in South America by U.S. Department of Agriculture entomologists resulted in the introductions of three species of insects into the United States for control of alligatorweed. Agasicles hygrophila (Coleoptera: Chrysomelidae) was first introduced in 1964, Amynothrips andersoni (Thysanoptera: Phlaeothripidae) in 1967, and Vogtia malloi (Lepidoptera: Pyralidae: Phycitinae) in 1971. These insects are now providing substantial control of alligatorweed over the entire range where the weed occurred as an aquatic plant problem. It is our contention that alligatorweed will cease to be an important aquatic weed and only rarely will be found in pure stands in any significant proportions in the United States of America.