Biological control of water hyacinth on Lake Victoria, Kenya.

The Kenya Agricultural Research Institute (KARI) imported 12 800 curculionid weevils (Neochetina spp.) from Benin, Uganda, South Africa and Australia for biological control of water hyacinth between 1993 and1998. In 1996, KARI’s rearing and quarantine facility at the National Agricultural Research Centre, Muguga, provided initial “breeding stock” to another rearing facility at the National Fibre Research Centre, Kibos, near Lake Victoria. To date, 36 500 weevils and 42 000 weevil eggs have been produced from Kibos. About 2000 weevils were produced each month from plants grown in plastic basins, galvanized corrugated iron sheet tanks and a polypropylene rearing pool. Between January 1997 and August 1998, KARI released 36 250 Neochetina weevils at 27 sites and redistributed 7 800 weevils along the Kenyan Lake Victoria shoreline. Visual observations and a pre- and post release sampling protocol have been used to monitor the establishment, spread and impact of Neochetina weevils on water hyacinth. Weevils are established at 5 sites and have spread as far as 50 km away from release sites. Preliminary quantitative data from 5 sites indicate a reduction in leaf length, lamina area and fresh weight at several sites and general increases in larval mining, feeding scars and adult weevil density.