These efforts set the stage for the most dramatic and well-known early application of a beneficial organism in the United States—the introduction of the Australian ladybird beetle (Rodolia cardinalis) to control the cottony-cushion scale (Icerya purchasi) in California. Throughout the 1880s, the cottony-cushion scale devastated the California citrus industry; by 1890, all scale infestations were under control following release of the ladybird beetle. This success was credited with saving the California citrus industry and catalyzed the expansion of biological control of other pests, including other arthropods, weeds, and diseases (DeBach and Rosen, 1991).
In the 1930s the prickly pear cactus (Opuntia spp.) was successfully controlled by a weed-feeding scale (Dactylopius opuntiae) on Santa Cruz Island off the coast of California (Goeden, 1993; Turner, 1992). One of the most notable achievements, however, occurred on rangeland where devastation by Klamath weed (Hypericum perforatum) so decreased land values that ranchers were not allowed to use their ranches as collateral to borrow money for chemicals to control the noxious weed. In 1946 the arthropods Chrysolina hyperici and C. quadrigemina were released and by 1956 had consumed 99 percent of the Klamath weed, increasing the price of land 300 to 400 percent (DeBach and Rosen, 1991).
The first organized attempt at biological control of an aquatic weed was directed against alligator weed (Alternanthera philoxeroides). More than 30 arthropods that parasitize this weed were found in South America in the weed's native range. Of these organisms, a flea beetle (Agasicles), was found to be safe and potentially effective and was introduced into the United States. Today, alligator weed remains under check in most of the South; however, the effectiveness of the flea beetle has been reduced in Mississippi as a result of extensive aerial spraying of chemical insecticides, and the flea beetles alone are usually not sufficient to manage this weed in high visibility areas such as golf course ponds and irrigation canals.
For water hyacinth, plant pathogens were suggested as possible biocontrol organisms as early as the 1930s in India. It was not until 1970, however, that a serious commitment was made by the University of Florida, the U.S. Army Corps of Engineers, and Florida Department of Natural Resources to explore the potential of microbial pathogens to control aquatic weeds. Several pathogens of alligator weed, water hyacinth, hydrilla, and Eurasian water milfoil were soon discovered, and three fungi—Cercospora rodmanii, Fusarium culmorum, and Mycoleptodiscus terrestris—were studied in detail for development as bioherbicides for water hyacinth, hydrilla, and Eurasian water milfoil, respectively, in Florida, Mississippi, and Massachusetts (Charudattan, 1990a).