Submitted to: Weed Biological Control with Arthropods in the Tropics - Towards Sustainability
Publication Type: Book / chapter
Publication Acceptance Date: 11/25/2007
Publication Date: 1/8/2009
Citation: Julien, M., Hill, M., Tipping, P.W. 2009. Salvinia molesta . Weed Biological Control with Arthropods in the Tropics - Towards Sustainability. 378-407. Interpretive Summary: Salvinia molesta D.S. Mitchell (salvinia) is a floating water fern of tropical and subtropical distribution worldwide. Its centre of origin is south-eastern Brazil and it is an extremely important invasive species and its biological control is an extraordinary, contemporary, success story. The rapid growth response by S. molesta ensures its weedy status in practically all natural situations from the most pristine to the most eutrophic water-bodies. Just a few S. molesta plants are all that is necessary to start a major infestation over vast areas. The success of the salvinia weevil as a biological control agent has been repeated in a range of countries, climates and habitats. There have been no reported adverse effects on other organisms during or following biological control of S. molesta. Therefore the first priority for the management of S. molesta should always be the release of the salvinia weevil.
Technical Abstract: Salvinia molesta is a free-floating aquatic fern. It has a horizontal stem that lies at or just below the water surface. Buoyancy is facilitated by the formation of aerenchyma tissue in the stems and leaves. Reproduction is entirely asexual: colony increase is through vegetative growth and the spread occurs only via movement of viable fragments (nodes or apical buds) and, therefore, S. molesta represents one massive clone worldwide. The native range of S. molesta encompasses a relatively small area in south-eastern Brazil in the States of São Paulo, Paraná, Santa Catarina and Rio Grande do Sul, between 24o 05’S and 32o 05’S; up to 200 km inland and up to 500 m altitude. It grows in wetland communities; natural lagoons and swamps, along the margins of streams and rivers, and in artificial dams and drainage channels. Its exotic range is cosmopolitan tropical, sub-tropical in every continent and in some warm temperate regions such as parts of southern Africa, the United States, and southern Australia. Infestations of S. molesta prevent light penetration, reduce oxygenation, increase carbon dioxide and hydrogen sulphide, smother aquatic flora, and displace aquatic fauna by altering habitats, destroying niches, and reduce or eliminate food sources (food plants, benthic biota and other fauna). Persistent mats often support other vegetation resulting in the formation of sudds which increase sedimentation and block water flow. Integrated strategies may be required to manage this weed. However, they should always include biological control. Even in less than optimal climates, once the salvinia weevil (Cyrtobagous salviniae) is established it is probable that it will reduce S. molesta growth rates and biomass accumulation. This will assist other forms of control if they are required; there will be less weed to treat or treatment will be required less often. In cases where thick mats have formed or sudds developed, breaking those up with herbicides will assist biological control. These situations are not the norm. In most situations S. molesta can be effectively and efficiently managed by release of the salvinia weevil. The biological control of S. molesta is an extraordinary success story with a single weevil species.