Biological Control Agents of Hydrilla Verticillata; Final Report on Surveys in East Africa, 1981-1984.
COMMONWEALTH INST OF BIOLOGICAL CONTROL SLOUGH (ENGLAND)
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Since its introduction into Florida in the early 1960s, the submerged aquatic plant Hydrilla verticillata has become a serious weed problem in the waterways of the southern United States. Since East Africa forms part of the natural distribution of hydrilla, a search for potential biological control agents in the region was carried out by the Commonwealth Institute of Biological Control from 1981 to 1984. Hydrilla was found to have a wide but disjunct distribution in Uganda Lake Kioga, Rwanda Lake Bulera and Mukungwa River, and Burundi Lake Tanganykia. In Kenya, despite an intensive search, only a single population, probably of exotic origin, was found. The range of the plant appears to have been reduced especially in Lake Victoria, probably by man-made changes in the environment. In East Africa hydrilla appears to be nonaggressive, and plants in most habitats are small in stature, forming mats on the hydrosoil and rarely reaching the surface. Plant growth appears in general to be constrained by fish grazing, but in Lake Tanganyika hydrilla is seasonally attacked by larvae of a chironomid which destroys many of the apical meristems and curtails upward growth of the plant. This species was not successfully reared, but should be further studied for possible introduction into the United States as it is damaging to hydrilla and may be specific for hydrilla. Pyralid larvae were found on hydrilla at one site but these were not damaging, and the plant was not a preferred host in that region.