Water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae), is the most important aquatic weed in South Africa, where ii has been subjected to biological control. The first biological control agent, Neochetina eichhorniae Warner, was released in 1974, but the project was terminated three years later and restarted in 1985. In this review, we focus on the biological and integrated control initiatives undertaken during the 1990s. We discuss the efficacy of the five arthropod natural enemies that have become established, namely the leaf-feeding weevils N. eichhorniae and N. bruchi Hustache, the petiole-mining moth Niphograpta albiguttalis (Warren) (= Sameodes albiguttalis Warren), the leaf-sucking bug Eccritotarsus catarinensis (Carvalho) and the leaf-mining mite Orthogalumna terebrantis Wallwork. The use of fungal pathogens as natural enemies for water hyacinth is the subject of a separate review in this issue. We consider the factors that have constrained the impact of the arthropod agents, notably (i) probable incompatibility with the range of climatic conditions in which the weed proliferates, (ii) high eutrophic levels of the waters invaded by the weed, (iii) periodic removal of weed and natural enemy populations through flooding and (iv) inappropriate integration of the agents with chemical control operations. Additional arthropod natural enemies that have been, or are being considered for release in South Africa are discussed, in particular the leaf- and petiole-mining moths Bellura densa Walker and Xubida infusella (Walker) (= Acigona infusella (Walker)), the grasshopper Cornops aquaticum (Bruner) and the petiole-mining fly Thrypticus sp. We conclude that enhancement of the biological control programme against water hyacinth in South Africa depends on (i) further releases to establish all five agents throughout the weed's range, (ii) studies on complementary new natural enemies for possible introduction and (iii) implementation of integrated management plans on a site-specific basis.
