BOX 4.7 LAKE BALDWIN, FLORIDA

Lake Baldwin is an 80-ha eutrophic lake located on the Orlando Ridge in Orlando, Florida (Canfield et al., 1983). The lake was stocked with 34 grass carp (each >394mm length, 0.8 kg) per hectare of hydrilla during summer and fall of 1978. An earlier stocking of fingerling grass carp in 1974 failed to control hydrilla, presumably because of high predation pressure on the fingerlings. Shireman and Maceina (1981) reported that hydrilla was nearly eradicated 2 years after the second stocking. According to these authors, hydrilla control was evident when grass carp biomass reached 130 kg of fish per hectare of hydrilla beds. Phytoplankton chlorophyll increased from approximately 5 µg per liter before stocking to levels as high as 30 µg per liter after aquatic plants had been eradicated (Canfield et al., 1983). Secchi disk transparency readings decreased from 6 m during the height of hydrilla infestation to approximately 1.5 m after hydrilla had been eradicated by grass carp. Chlorophyll a and total alkalinity also increased in the lake after hydrilla had been controlled. The long-term effects of eliminating the lake's macrophytes on total fish biomass and species composition could not be determined from a relatively short period of study after treatment but could be significant (Canfield et al., 1983).

the parental stock (Osborne, 1982; Shireman et al., 1983). This drawback has been overcome with the development of a sterile triploid form that has about the same feeding and growth characteristics as the fertile diploid form (Wiley and Wike, 1986).

Insect control of alligator weed and water hyacinth has been effective in Florida, Alabama, Mississippi, Texas, Louisiana, and Georgia. Alligator weed is controlled primarily by two insects: Agasicles hygrophila, commonly known as the alligator weed flea bettle, and Vogtia malloi pastrana, commonly known as the alligator weed stem borer. The species of insects involved include Sameodes ilbiguttalis (Warren) (Lepidoptera: Pyralidae) and Neochetina eichhornia Warner and N. bruchi Hustache (Coleoptera: Curculionidae). Techniques have been developed to concentrate the insects, allowing their reproduction, population growth, and subsequent spread through the lake. A characteristic



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