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Water SA
versión On-line ISSN 1816-7950
versión impresa ISSN 0378-4738
Water SA vol.34 no.2 Pretoria feb. 2008
Optimisation of Bacillus thuringiensis var. israelensis (Vectobac®) applications for the blackfly control programme on the Orange River, South Africa
NA Rivers-MooreI; S BangayII; RW PalmerIII
IInstitute for Water Research, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
IIDepartment of Computer Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa
IIINepid Consultants, PO Box 4349, White River 1240, South Africa
ABSTRACT
The Orange River, South Africa's largest river, is a critical water resource for the country. In spite of the clear economic benefits of regulating river flows through a series of impoundments, one of the significant undesirable ecological consequences of this regulation has been the regular outbreaks of the pest blackfly species Simulium chutteri and S. damnosum s.l. (Diptera: Simuliidae). The current control programme, carried out by the South African National Department of Agriculture, uses regular applications, by helicopter, of the target-specific bacterial larvicide Bacillus thuringiensis var. israelensis. While cost-benefit analyses show significant benefits to the control programme, benefits could potentially be further increased through applying smaller volumes of larvicide in an optimised manner, which incorporates upstream residual amounts of pesticide through downstream carry. Using an optimisation technique applied in the West African Onchocerciasis Control Programme, to a 136 km stretch of the Orange River which includes 31 blackfly breeding sites, we demonstrate that 28.5% less larvicide could be used to potentially achieve the same control of blackfly. This translates into potential annual savings of between R540 000 and R1 800 000. A comparison of larvicide volumes estimated using traditional vs. optimised approaches at different discharges, illustrates that the savings on optimisation decline linearly with increasing flow volumes. Larvicide applications at the lowest discharge considered (40 m3∙s-1) showed the greatest benefits from optimisations, with benefits remaining but decreasing to a theoretical 30% up to median flows of 100 m3∙s-1. Given that almost 70% of flows in July are less than 100 m3∙s-1, we suggest that an optimised approach is appropriate for the Orange River Blackfly Control Programme, particularly for flow volumes of less than 100 m3∙s-1. We recommend that trials be undertaken over two reaches of the Orange River, one using the traditional approach, and another using the optimised approach, to test the efficacy of using optimised volumes of B.t.i.
Keywords: Simulium chutteri, Simulium damnosum, Orange River, flow regulation, Bacillus thuringiensis var. israelensis, optimisation
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References
AHO AV, HOPCROFT JE and ULLMAN JD (1983) Data Structures and Algorithms. Addison-Wesley, Reading, Mass. [ Links ]
BOISVERT M, BOISVERT J and AUBIN A (2001) Factors affecting black fly larval mortality and carry of two formulations of Bacillus thuringiensis subsp. israelensis tested in the same stream during a 3-year experiment. Biocontrol Sci.Technol. 11 711-725. [ Links ]
CHALIFOUR A, BOISVERT J and BACK C (1990) Optimization of insecticide treatments in rivers: Application of graph theory for planning a black fly control program. Can. J. Fish. Aquat. Sci. 47 2049-2056. [ Links ]
DWAF (2006) Department of Water Affairs and Forestry. Private Bag X313, Pretoria, 0001, South Africa. [ Links ]
FORD LR JR (1956) Network Flow Theory. The Rand Corp. 293 pp. [ Links ]
MIDGLEY DC, PITMAN WV and MIDDLETON BJ (1994) Surface Water Resources of South Africa 1990. Volume III: Orange-Namaqualand. WRC Report No. 298/3.1/94. Water Research Commission, Pretoria, South Africa. [ Links ]
MULLINS W (2007) Cost-benefit analysis. In: Palmer RW, N Rivers-Moore, W Mullins, V McPherson and L Hattingh (authors) Guidelines for Integrated Control of Pest Blackflies along the Orange River. WRC Report No. 1558/1/07. Water Research Commission, Pretoria, South Africa. [ Links ]
NEL J (2006) Personal communication. Agriculture Control Programme, Department of Agriculture: Directorate of Resource Conservation, Pretoria, South Africa. [ Links ]
O'KEEFFE JH and DE MOOR FC (1988) Changes in the physico-chemistry and benthic invertebrates of the Great Fish River, South Africa, following an interbasin transfer of water. Regulated Rivers: Res. Manage. 2 39-55. [ Links ]
PALMER RW (1994) A rapid method of estimating the abundance of immature blackflies (Diptera: Simuliidae). Onderstepoort J. Vet. Res. 61 117-126. [ Links ]
PALMER RW (1997) Principles of Integrated Control of Blackflies (Diptera: Simuliidae) in South Africa. WRC Report No. 650/1/97. Water Research Commission, Pretoria, South Africa. [ Links ]
PALMER RW (1998) An overview of black fly (Diptera: Simuliidae) control in the Orange River, South Africa. Isr. J. Entomol. 32 99-110. [ Links ]
PALMER RW, EDWARDES M and NEVILL EM (1996) Downstream carry of larvicides used in the control of pest blackflies (Diptera: Simuliidae) in the Orange River, South Africa. J. Vector Ecol. 21 (1) 37-47. [ Links ]
SNADDON CD and DAVIES BR (1998) A preliminary assessment of the effects of a small South African inter-basin water transfer on discharge and invertebrate community structure. Regulated Rivers: Res. Manage. 14 421-441. [ Links ]
SUN DEVELOPER NETWORK (SDN) (2006) <http://java.sun.com WILSON MD, AKPABEY FJ, OSEI-ATWENEBOANA MY, BOAKYE DA, OCRAN M, KURTAK DC, CHEKE RA, MENSAH GE, BIRKHOLD D and CIBULSKY R (2005) Field and laboratory studies on water conditions affecting the potency of Vectobac®(Bacillus thuringiensis serotype H-14) against larvae of the blackfly, Simulium damnosum. Med. Vet. Entomol. 19 1-9. [ Links ]
Correspondence:
+27 46-6222428
Fax: +27 46 622-9427
E-mail: nick@iwr.ru.ac.za
Received 19 April 2007
Accepted in revised form 21 January 2008