Hydrilla verticillata threatens South African waters
J.A. Coetzee1 and P.T. Madeira2
Summary South Africa’s inland water systems are currently under threat from hydrilla, Hydrilla verticillata L. Royle (Hydrocharitaceae), the worst submerged aquatic weed in the USA. The presence of the weed was confirmed for the first time in South Africa in February 2006, on Pongolapoort Dam in KwaZulu-Natal. An aerial survey revealed that the infestation on this dam covers approximately 600 ha, which is far greater than initially thought. Despite reports that it may be present in other water bodies, surveys have shown that it is restricted to Pongolapoort Dam. We conducted a boater survey which showed that there is significant potential for this devastating weed to spread beyond Pongo- lapoort Dam, and containment of hydrilla is of utmost priority. Research into the suitability of the already established biological control agents, Hydrellia pakistanae Deonier and H. balciunasi Bock (Diptera: Ephydridae), from the USA, as potential agents in South Africa, is also being conducted. However, the South African hydrilla biotype is different from the biotypes in the USA, and this needs to be borne in mind when considering which agents to release.
Keywords: potential spread, management, genetic analysis.
Introduction Current distribution of The confirmation of Hydrilla verticillata L. Royle hydrilla in South Africa (Hydrocharitaceae) (hydrilla) in South Africa from and potential for spread Pongolapoort Dam, KwaZulu-Natal province (KZN), in early 2006 (L. Henderson, personal communication, Hydrilla is one of the most problematic submerged 2006) prompted immediate action to contain and con- plants worldwide, invading both tropical and temperate trol this weed, and prevent further spread to other wa- regions because of its tolerance to a wide range of envi- ter bodies around South Africa. At present, it appears ronmental conditions (Cook and Lüönd, 1982). It is not that hydrilla is restricted to Pongolapoort Dam, which clear how or when hydrilla entered South Africa, and is the centre of a multimillion rand tourist industry. It so the first step in the hydrilla biocontrol programme in is imperative that we gain an understanding of the dy- South Africa was to determine the extent of its distri- namics of the hydrilla invasion in South Africa, and po- bution. Following reports that hydrilla’s presence was tential for its control, because there is a knowledge gap suspected in a number of water bodies in KZN, both in South Africa surrounding submerged aquatic plants, aerial and boat surveys were undertaken, which con- particularly from a biological control aspect. firmed that hydrilla is currently restricted to an area of about 600 ha in Pongolapoort Dam. However, heavy rains in early January 2007 resulted in the flooding of this area, and the dam increased in capacity from 73% to 92% full in 1 week. The possibility that hydrilla 1 ARC–Plant Protection Research Institute, P/Bag X134, Queenswood has spread throughout the dam, and into the Pongola 0121, South Africa. Current address: Department of Zoology and En- tomology, Rhodes University, PO Box 94, Grahamstown 6140, South River below should not be ruled out, and warrants fur- Africa. ther investigation. 2 USDA-ARS, Invasive Plant Research Laboratory, 3205 College Av- While containment of hydrilla in Pongolapoort Dam enue, Fort Lauderdale, FL 33314, USA. is currently the main control strategy in South Africa, Corresponding author: J.A. Coetzee
665 XII International Symposium on Biological Control of Weeds boaters and fishermen (Balciunas et al., 2002) as frag- Fluridone does have non-target side effects on other ments of the plant get caught in anchors and propellers aquatic vegetation and fish, which has led to sublethal and are then transported between water bodies. It is doses being applied as this minimizes these effects, and therefore very likely that hydrilla may spread through- is more cost-effective. However, hydrilla has become out South Africa in this manner, particularly because resistant to these doses in the USA, which has compli- Pongolapoort Dam attracts thousands of tourists annu- cated control programmes (Michel et al., 2004; Dayan ally, and because it is home to the annual Tiger Fish- and Netherland, 2005). So it becomes a risk–benefit is- ing Festival, the biggest tiger fishing competition in sue in South Africa – is it worth using a lethal dose the southern hemisphere that attracts fishermen from that will remove large amounts of the plant, but that all over South Africa, and neighbouring Swaziland and will impact the fauna and flora in the dam, against the Mozambique. potential of resistance developing if sublethal doses are Fishermen are primarily responsible for hydrilla’s used, thereby ruling out the most effective control strat- spread in the USA. Therefore we conducted a survey at egy against it? the annual Tiger Fishing Festival in September 2006 to The most sustainable long-term strategy to control determine the potential for hydrilla to spread through- hydrilla should be biological control. The option of us- out South Africa by assessing boating behaviour of the ing the two species of ephydrid flies, Hydrellia paki- fishermen, and whether they were aware of the pres- stanae Deonier and H. balciunasi Bock (both Diptera: ence of hydrilla on the dam. One hundred sixty-three Ephydridae) as potential control agents against hydrilla fishermen were asked questions from a structured ques- in South Africa is being investigated, because these are tionnaire. The results showed that 51% of the fishermen the only two agents that have established in the USA interviewed only used their boats once on Pongolapoort (Center et al., 1997; Bennett and Buckingham, 2000; Dam, and that was at the September competition. The Grodowitz et al., 2000; Wheeler and Center, 2001). In results also showed that 14.1% of the fishermen used addition, the weevil, Bagous hydrillae O’Brien (Cole- their boats only on Pongolapoort Dam between Janu- optera: Curculionidae), which was tested and released ary 2005 and September 2006, and 20 respondents in the USA to control hydrilla but never established (12.2%) never used their boats anywhere except once because it requires periods of drought for pupation at the 2006 fishing competition, between January 2005 (Grodowitz et al., 2000), is being considered as a and September 2006. control agent in South Africa because drawdowns are However, analysis of the number of times fisher- implemented on Pongolapoort dam. Permits have been men used their boats in South Africa highlighted that granted to import the flies and the weevil into South dams outside of KZN were visited more frequently Africa from the USA, so that host specificity testing than those in KZN, and the majority of fishermen trav- may commence. eled between 200 and 800 km to reach their fishing Expanded surveys are also being conducted by both destinations, emphasizing the potential for hydrilla to the USDA-ARS and CSIRO to find additional control spread around South Africa. Even though a contain- agents for hydrilla in the USA (Overholt and Wheel- ment strategy is in place on Pongolapoort Dam, this er, 2006), following the discovery that infestations of survey stressed that more water bodies in South Africa hydrilla are resistant to fluridone (Michel et al., 2004; need to be assessed for the presence of hydrilla as a Puri et al., 2007). Surveys in Burundi, Uganda and result of boating activities before the fishing competi- other central and east African countries, and in Suma- tion in September. tra and China have found promising agents (Overholt and Wheeler, 2006), which could be considered as ad- Management options ditional control agents in South Africa. Mechanical and chemical control has been the most widely used control methods in the USA, although Identification and origin of the their success is varied. Typically, mechanical control introduced biotype using is time-consuming and only offers temporary control, chloroplastic markers and its use has been dissuaded in South Africa, par- ticularly because new infestations can result from plant Hydrilla is a widely distributed species whose range fragments. Until a biocontrol programme can be imple- extends from New Zealand and Australia, through mented, chemical control is currently the most favour- Southeast Asia, north through China, into Siberia, and able option for hydrilla. It should be controlled using west into Pakistan, and it also has a local and disjointed herbicides as soon as possible because it is confined to range in Africa and northern Europe (Cook and Lüönd, only one system. The most effective herbicide to date 1982). Studies have identified more than 28 different against hydrilla in the USA is fluridone, which has been hydrilla biotypes, which could have important con- widely used for large-scale control (Dayan and Nether- sequences for biological control of the plant in South land, 2005). Trials with this herbicide will commence Africa. Four major biotype clusters and one minor out- as soon as it is imported into South Africa. lier cluster have been identified (Madeira et al., 1997,
666 Hydrilla verticillata threatens South African waters
1999). The USA has two hydrilla biotypes – a dioe- Alien Species Programme of KwaZulu-Natal Depart- cious strain that clusters closely with an Indian strain, ment of Agriculture and Environmental Affairs is ac- and a monoecious strain that clusters closely with an knowledged for financial assistance. accession from Korea (Madeira et al., 1997). Several biocontrol agents have been released in the USA, but only the leaf mining fly H. pakistanae References is causing significant damage (Wheeler and Center, 2001). Regional variation in both the host plant and the Balciunas J.K., Grodowitz, M.J., Cofrancesco, A.F. and Shearer, J.F. (2002) Hydrilla. In: Van Driesche, R., Lyon, control agent populations could potentially affect the S., Blossey, B., Hoddle, M. and Reardon, R. (eds) Bio- effectiveness of new releases. It is therefore essential logical Control of Invasive Plants in the Eastern United in any biocontrol programme to know which biotype States. USDA Forest Service, Morgantown, WV, USA, is being dealt with to maximize the efficacy of control pp. 91–114. agents, by selecting agents from the same area as the Bennett, C.A. and Buckingham, G.R. (2000) The herbivorous plant biotype. insect fauna of a submersed weed, Hydrilla verticillata Therefore, samples of South African hydrilla were (Alismatales: Hydrocharitaceae). In: Spencer, N.R. (ed.) analysed using the trnL intron and trnL-F intergenic Proceedings of the X International Symposium on Bio- spacer of the chloroplast to determine to which major logical Control of Weeds, July 4–14, 1999. Montana State cluster of worldwide hydrilla the South African hy- University, Bozeman, MT, USA, pp. 307–313. drilla belongs (Madeira et al., 2007). In the sequencing Center, T.D., Grodowitz, M.J., Cofrancesco, A.F., Jubinsky, G., Snoddy, E. and Freedman, J.E. (1997) Establishment it was identical to Malaysian and Indonesian samples. of Hydrellia pakistanae (Diptera: Ephydridae) for the This biotype is also monoecious, and produces copi- biological control of the submersed aquatic plant Hydrilla ous numbers of flowers, pollen, seedpods and seeds. verticillata (Hydrocharitaceae) in the southeastern United South African hydrilla is therefore very different from States. Biological Control 8, 65–73. hydrilla in the USA, and the control agents currently in Cook, C.D.K. and Lüönd, R. (1982) A revision of the genus use in the USA might not be as suitable to the biotype Hydrilla (Hydrocharitaceae). Aquatic Botany 13, 485–504. in South Africa. Dayan, F.E. and Netherland, M.D. (2005) Hydrilla, the per- Biotype analysis is also interesting from an introduc- fect aquatic weed, becomes more noxious than ever. Out- tion point of view. By determining to which cluster hy- looks on Pest Management 16, 277–282. drilla belongs, inferences about how it was introduced Grodowitz, M.J., Doyle, R. and Smart, R.M. (2000) Potential to South Africa can be made. Hydrilla was introduced use of insect biocontrol agents for reducing the competi- tive ability of Hydrilla verticillata. ERDC/EL SR-00-1. into the USA via the aquarium trade (Schmitz et al., US Army Engineer Research and Development Center, 1991), and it is likely that this was also the mode of Vicksburg, MS, USA, 27 pp. introduction into South Africa. Interestingly, the major- Madeira, P.T., Van, T.K., Steward, K.K. and Schnell, R.J. ity of aquarium plants imported into South Africa come (1997) Random amplified polymorphic DNA analysis of from Singapore, Malaysia, which is where the South the phenetic relationships among world-wide accessions African hydrilla biotype is most closely related. of Hydrilla verticillata. Aquatic Botany 59, 217–236. Madeira, P.T., Van, T.K. and Center, T.D. (1999) Integration of five Southeast Asian accessions into the world-wide Conclusions phenetic relationships of Hydrilla verticillata as eluci- Much progress has been made in understanding the bi- dated by random amplified polymorphic DNA analysis. ology of hydrilla, the nature of the infestation and the Aquatic Botany 63, 161–167. Madeira, P.T., Coetzee, J.A., Center, T.D., White, E.E. and potential for the weed to spread further in South Africa. Tipping, P.W. (2007) The origin of Hydrilla verticillata We also know what the biotype is, but little is known recently discovered at a South African dam. Aquatic Bot- about the flowering and reproductive phenology of this any 87, 176–180. biotype in South Africa. This calls for further study Michel, A., Scheffler, B.E., Arias, R.S., Duke, S.O., Netherland, in both the laboratory and the field in the upcoming M. and Dayan F.E. (2004) Somatic mutation-mediated months. Furthermore, the certainty that the Hydrellia evolution of herbicide resistance in the non-indigenous flies and Bagous hydrillae will be suitable against the invasive plant hydrilla (Hydrilla verticillata). Molecular South African biotype cannot be guaranteed. It seems Ecology 13, 3229–3237. that the best way forward would be for South Africa Overholt, B. and Wheeler, G. (2006) Renewed efforts to iden- to undertake surveys in Sumatra and China, and other tify hydrilla biocontrol agents in Asia and Africa. Biocon- Southeast Asian countries such as Thailand, Indonesia trol News and Information 27, 53–53. Puri, A., MacDonald, G.E. and Haller, W.T. (2007) Stability and Malaysia, from where the biotype originates. of fluridone-resistant hydrilla Hydrilla( verticillata) bio- types over time. Weed Science 55, 12–15. Acknowledgements Schmitz, D.C., Nelson, B.V., Nall, L.E. and Schardt, J.D. (1991) Exotic aquatic plants in Florida: A historical per- Angela Bownes (ARC–Plant Protection Research In- spective and review of present aquatic plant regulation stitute) is thanked for help in the field. The Invasive program. In: Center, T.D., Doren, R.F., Hofstetter, R.L.,
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Myers, R.L. and Whiteaker, L.D. (eds) Proceedings of a Wheeler, G.S. and Center, T.D. (2001) Impact of the biologi- Symposium on Exotic Pest Plants, November 2–4, 1988, cal control agent Hydrellia pakistanae (Diptera: Ephydri- Miami, FL. United States Department of the Interior, Na- dae) on the submersed aquatic weed Hydrilla verticillata tional Park Service, Washington, DC, USA, pp. 303–336. (Hydrocharitaceae). Biological Control 21, 168–181.
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