Biological control of water hyacinth with arthropods: a review to 2000.

Water hyacinth, native to the Amazon River, invaded the tropical world over the last century and has become an extremely serious weed. The search for biological control agents began in the early 1960s and continues today. Six arthropod species have been released around the world. They are: two weevils, Neochetina bruchi and N. eichhorniae ; two moths, Niphograpta albiguttalis and Xubida infusellus ; a mite Orthogalumna terebrantis ; and a bug Eccritotarsus catarinensis . The mite and X. infusellus have not contributed to control and the bug is under evaluation following recent releases in Africa. The two weevils and the moth N. albiguttalis have been released in numerous infestations since the 1970s and have contributed to successful control of the weed in many locations. It is timely to assess their impact on water hyacinth and, to help in planning future strategies, to identify the factors that contribute to or mitigate against successful biological control. Although the search for new agents continues, and as a result biological control will likely be improved, this technique alone is unlikely to be successful in all of the weed’s habitats. It is important that whole-of-catchment management strategies be developed that integrate biological control with other control techniques. The aims of such strategies should be to achieve the best possible control using methods that are affordable and sustainable; hence the need to develop strategies using biological control as the base component. W ATER hyacinth apparently became a problem in the USA following its distribution to participants in the 1884 New Orleans Cotton Exposition. By the early 1900s it was widespread in the southern states. During the same period it spread through the tropics of other continents and now reaches around the world and north and south as far as the 40° latitudes (Center 1994). More recently it spread into the many waterways of Africa and has expanded rapidly, probably in response to high nutrient conditions, to cause serious problems. To combat the problems caused by the weed, efforts to control its spread and to reduce its biomass have been many and varied and include weed management methods such as physical removal, application of herbicides and release of biological control agents. Utilisation of the weed for commercial and subsistence purposes has also been widely considered. It is now generally recognised that physical and chemical controls have very limited application in most countries because of their high cost and low sustainability. Utilisation has never developed into sustainable activities other than localised cottage industries or to support very poor communities in subsistence existences such as the production of biogas. Only small amounts of water hyacinth can be utilised in such activities, which should never be confused with control. Neither should the potential for utilisation prevent the implementation of control strategies (Harley et al. 1996; Julien et al. 1996). The cost of water hyacinth to communities far outweighs the benefits that might occur through utilisation. In general, even when the weed is successfully managed there is likely to be sufficient present to support the small-scale utilisation activities that persist. * CSIRO Entomology, 120 Meiers Road, Indooroopilly, Queensland 4068, Australia. Email: mic.julien@brs.ento. csiro.au