Development of environmental tools for anopheline larval control

Abstract

Background: Malaria mosquitoes spend a considerable part of their life in the aquatic stage, rendering them vulnerable to interventions directed to aquatic habitats. Recent successes of mosquito larval control have been reported using environmental and biological tools. Here, we report the effects of shading by plants and biological control agents on the development and survival of anopheline and culicine mosquito larvae in man-made natural habitats in western Kenya. Trials consisted of environmental manipulation using locally available plants, the introduction of predatory fish and/or the use of Bacillus thuringiensis var. israelensis (Bti) in various combinations.

Results: Man-made habitats provided with shade from different crop species produced significantly fewer larvae than those without shade especially for the malaria vector Anopheles gambiae. Larval control of the African malaria mosquito An. gambiae and other mosquito species was effective in habitats where both predatory fish and Bti were applied, than where the two biological control agents were administered independently.

Conclusion: We conclude that integration of environmental management techniques using shade-providing plants and predatory fish and/or Bti are effective and sustainable tools for the control of malaria and other mosquito-borne disease vectors.

Figure 1

Abundance of late instar larvae of anopheline species in habitats with: a) arrow roots growing in water, (b) arrow roots growing along water banks, (c) sweet potatoes along water banks, (d) couch grass in the water, (e) Azolla on water surface, and (f) control without plant cover, in Nyalenda.

Figure 2

Larval distribution of Anopheles gambiae and An. coustani in the control and habitats provided by different plant cover types, expressed as a percentage of the total number of larvae collected.

Figure 3

Anopheles gambiae, An. funestus and An. coustani larval distribution in the (A) ponds and (B) canal man-made habitats under different treatments expressed as a percentage of the total number of larvae recorded.