Abstract
BackgroundBiological control methods are once again being given much research focus for malaria vector control. This is largely due to the emerging threat of strong resistance to pesticides. Larvivorous fish have been used for over 100 years in mosquito control and many species have proved effective. In the western Kenyan highlands the larvivorous fish Oreochromis niloticus L. (Perciformes: Cichlidae) (formerly Tilapia nilotica) is commonly farmed and eaten but has not been previously tested in the field for malaria mosquito control.MethodsThis fish was introduced into abandoned fishponds at an altitude of 1,880 m and the effect measured over six months on the numbers of mosquito immatures. For comparison an untreated control pond was used. During this time, all ponds were regularly cleared of emergent vegetation and fish re-stocking was not needed. Significant autocorrelation was removed from the time series data, and t-tests were used to investigate within a pond and within a mosquito type any differences before and after the introduction of O. niloticus. Mulla's formula was also used on the raw data to calculate the percentage reduction of the mosquito larvae.ResultsAfter O. niloticus introduction, mosquito densities immediately dropped in the treated ponds but increased in the control pond. This increase was apparently due to climatic factors. Mulla's formula was applied which corrects for that natural tendency to increase. The results showed that after 15 weeks the fish caused a more than 94% reduction in both Anopheles gambiae s.l. and Anopheles funestus (Diptera: Culicidae) in the treated ponds, and more than 75% reduction in culicine mosquitoes. There was a highly significantly reduction in A. gambiae s.l. numbers when compared to pre-treatment levels.ConclusionThis study reports the first field trial data on O. niloticus for malaria mosquito control and shows that this species, already a popular food fish in western Kenya, is an apparently sustainable mosquito control tool which also offers a source of protein and income to people in rural areas. There should be no problem with acceptance of this malaria control method since the local communities already farm this fish species.
Highlights
Biological control methods are once again being given much research focus for malaria vector control
Concern about the threat of strong forms of resistance [1] has stimulated renewed interest in alternative control methods including biological control and biopesticides. At present these methods are only operational against mosquito immatures [2,3,4,5], the best known being the use of Bacillus thuringiensis var. israelensis (Bti)
High percentage reductions were found for A. gambiae s.l. and A. funestus
Summary
Biological control methods are once again being given much research focus for malaria vector control This is largely due to the emerging threat of strong resistance to pesticides. Bti is effective against mosquito larvae [5] but cannot control the pupal stage, frequent repeat applications are needed [6] and it is expensive. Another biocontrol method, the use of larvivorous fish in appropriate water bodies, has been used in mosquito control for over 100 years [7] and can be effective [2,8,9,10]. One disadvantage is that larvivorous fish can only be used under certain conditions conducive to their survival
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