Biological Control Programs for Giant Salvinia:
History and Update on U.S. Efforts

Philip W. Tipping and Ted D. Center
USDA-ARS, Invasive Plant Research Laboratory
3205, College Ave., Ft. Lauderdale, FL 33314
09 June 2000

Salvinia molesta D. S. Mitchell, one of the world’s most invasive aquatic weeds, has recently become established in areas of east Texas and western Louisiana (Jacono 1999). This weed has been the target of classical biological control programs since the 1960's in Africa, Asia, and Australia (Room 1990). However, the first attempts were unsuccessful in Africa, India, Fiji, and Sri Lanka because of the misidentification of the plant as Salvinia auriculata Aublet (Thomas and Room, 1986, Julien and Griffiths 1998). Researchers surveyed S. auriculata in Guyana and Trinidad and found a small weevil identified as Cyrtobagous singularis Hustache (Coleoptera: Curculionidae) (Bennett 1966). Although C. singularis did establish in several areas, it had no effect on the infestations (Room 1990). Salvinia molesta was separated from S. auriculata in 1972 (Mitchell 1972) and its native range in Brazil was discovered in 1978 (Forno and Harley 1979). In 1980, what was thought to be a biotype of C. singularis collected from S. molesta in Brazil was introduced at Lake Moondarra in Australia and it proceeded to destroy more than 30,000 tons of S. molesta in less than one year (Room et al. 1981). Closer examination of the “biotype” resulted in its elevation to species status, namely Cyrtobagous salviniae Calder and Sands (Calder and Sands 1985). This new species reversed earlier failures and successful programs were conducted in Australia, Fiji, Ghana, Kenya, Malaysia, Papua New Guinea, the Republic of South Africa, Zambia, Zimbabwe, India, Botswana, Namibia, and Sri Lanka where control has been dramatic and rapid: in many cases S. molesta was reduced by more than 90% in less than a year following release of C. salviniae (Room 1990; Julien and Griffiths 1998).
The USDA-ARS Invasive Plant Research Laboratory located in Fort Lauderdale originally planned to import C. salviniae from Australia to release in Texas and Louisiana until several taxonomists confirmed its presence in Florida feeding on S. minima Baker, a naturalized close relative of S. molesta (Calder and Sands 1985, C. W. O’Brien, personal communication). Originally identified as C. singularis, this weevil was first detected in Florida in 1960 (Kissinger 1966). Jacono et. al (2001) examined the records of both C. salviniae and S. minima in the United States and conducted surveys to determine the geographic extent of C. salviniae on S. minima. They found C. salviniae abundantly in Florida but not in other states. Accordingly, in order to avoid the risk of introducing new pathogens or parasites from abroad, it was decided to release the Florida population of C. salviniae on S. molesta in Texas and Louisiana. The first releases were conducted in June, 1999 at research sites in both states. Several recoveries of adults have been made but no significant reduction of S. molesta occurred, except at one site. The S. molesta at that particular site in Liberty County, Texas, was heavily damaged and sank within the delineated release area. However, unlike examples in Australia where the damage continued outward from the release area on a rapidly moving front, new plants quickly replaced the destroyed material and similar damage did not recur (PWT, unpublished data).
The possibility of additional introductions of weevils from Australia by APHIS prompted us to conduct molecular testing comparing the D2 gene between Florida and Australian populations. This was done to provide a method of distinguishing one from the other in the field so as not to confuse the evaluation process. The D2 gene is a molecular tool for identifying cryptic or sibling species. Such species have diagnostic characteristics that are not easily perceived using traditional taxonomic techniques. Australian C. salviniae were collected from S. molesta at Wappa Dam in Queensland while Florida C. salviniae were collected from six sites in south Florida from S. minima. Although no variation was found within each population, some base pair differences were found between the two populations. The biological magnitude of these differences is not yet clear and further testing continues. However, one possibility is that the genus Cyrtobagous may comprise a complex of cryptic species associated with the Salviniaceae and that the south Florida weevils could be a new species, perhaps one that is specific to S. minima and poorly adapted to S. molesta. Further study is needed to clarify these relationships and their relevance to biological control. In the meantime, no more releases of the Florida population of weevils are planned.
The original plan of importing Australian weevils is now underway but any field releases of these weevils will be delayed until they are tested against representative North American plants. If these tests can be completed in a timely manner and are negative, i.e., the weevils do not feed on plants other than Salvinia, it is possible that field releases could be conducted sometime in 2001.

References Cited

Bennett, F. D. 1966. Investigations on the insects attacking the aquatic fern Salvinia sp. in Trinidad and northern South America. Proc. South. Weed Conf. 19: 497-504.

Calder, A. A., and D. P. A. Sands. 1985. A new Brazilian Cyrtobagous Hustache (Coleoptera: Curculionidae) introduced into Australia to control salvinia. J. Aust. Entomol. Soc. 24: 57-64.

Forno, I.W. and K.L.S. Harley. 1979. The occurrence of Salvinia molesta in Brazil. Aquatic Botany 6: 185-187.

Jacono, C.C. 1999. Salvinia molesta (Salviniaceae) new to Texas and Louisiana. Sida 18(3): 927-928.

Jacono, C.C., T. R. Davern and T.D. Center. 2001. The adventive status of Salvinia minima and S. molesta in the southern United States and the related distribution of the weevil Cyrtobagous salviniae. Castanea (in press).

Julien, M.H. and M.W. Griffiths. 1988. Biological Control of Weeds: a World Catalogue of Agents and their Target Weeds, Fourth Edition, CAB International.

Kissinger, D.G. 1966. Cyrtobagous Hustache, a genus of weevils new to the United States fauna (Coleoptera: Curculionidae: Bagoini). Coleopt. Bull. 20(4):125-127.

Mitchell, D. S. 1972. The Kariba weed: Salvinia molesta. Br. Fern Gaz. 10: 251-252.

Room, P. M., K. L. S. Harley, I. W. Forno, and D. P. A. Sands. 1981. Successful biological control of the floating weed Salvinia. Nature 294: 78-80.

Room, P. M., I. W. Forno, and M. F. J. Taylor. 1984. Establishment in Australia of two insects for biological control of the floating weed Salvinia molesta. Bull. Ent. Res. 74: 505-576.

Room, P. M. 1990. Ecology of a simple plant-herbivore system: biological control of Salvinia. Trends in Ecology & Evolution. 5: 74-79.

Thomas, P. A. & P. M. Room. 1986. Taxonomy and control of Salvinia molesta. Nature 320: 581-584.

HOME || FISC || CARS || NAS

U.S. Department of the Interior | U.S. Geological Survey
URL: http://salvinia.er.usgs.gov/
Page Contact Information: Buck Albert - Web Administrator
Page Last Modified: April 27 2005