Empowering rural communities for effective larval source management: A small-scale field evaluation of a community-led larviciding approach to control malaria in south-eastern Tanzania

Abstract

Introduction: Larval source management, particularly larviciding, is mainly implemented in urban settings to control malaria and other mosquito-borne diseases. In Tanzania, the government has recently expanded larviciding to rural settings across the country, but implementation faces multiple challenges, notably inadequate resources and limited know-how by technical staff. This study evaluated the potential of training community members to identify, characterize and target larval habitats of Anopheles funestus mosquitoes, the dominant vector of malaria transmission in south-eastern Tanzania.

Methods: A mixed-methods study was used. First, interviewer-administered questionnaires were employed to assess knowledge, awareness, and perceptions of community members towards larviciding (N = 300). Secondly community-based volunteers were trained to identify and characterize aquatic habitats of dominant malaria vector species, after which they treated the most productive habitats with a locally-manufactured formulation of the biolarvicide, Bacillus thuringiensis var. israelensis. Longitudinal surveys of mosquito adults and larvae were used to assess impacts of the community-led larviciding programme in two villages in rural south-eastern Tanzania.

Results: At the beginning of the program, the majority of village residents were unaware of larviciding as a potential malaria prevention method, and about 20 % thought that larvicides could be harmful to the environment and other insects. The trained community volunteers identified and characterized 360 aquatic habitats, of which 45.6 % had Anopheles funestus, the dominant malaria vector in the area. The preferred larval habitats for An. funestus were deep and had either slow- or fast-moving waters. Application of biolarvicides reduced the abundance of adult An. funestus and Culex spp. species inside human houses in the same villages, by 46.3 % and 35.4 % respectively. Abundance of late-stage instar larvae of the same taxa was also reduced by 74 % and 42 %, respectively.

Conclusion: This study demonstrates that training community members to identify, characterize, and target larval habitats of the dominant malaria vectors can be effective for larval source management in rural Tanzania. Community-led larviciding reduced the densities of adult and late-stage instar larvae of An. funestus and Culex spp. inside houses, suggesting that this approach may have potential for malaria control in rural settings. However, efforts are still needed to increase awareness of larviciding in the relevant communities.

Keywords: Biolarvicides; Community engagement; Ifakara health institute; Larval source management; Larviciding; Malaria control; Tanzania.

Fig. 1

Map showing two villages in the Kilombero Valley, south-eastern Tanzania where the study was conducted.

Fig. 2

Theoretical and practical training of the community members for identification and characterization of aquatic habitats and application of larviciding.

Fig. 3

Example of the common An. funestus larvae habitats found in Sululu and Igumbiro villages, south-eastern Tanzania.

Fig. 4

Effect of a single application of biolarvicides on abundance of adult An. funestus, An. arabiensis and Culex spp. inside houses in Sululu and Igumbiro villages, south-eastern Tanzania.

Fig. 5

Densities of early- and late-instar larvae of An. funestus, An. arabiensis and Culex spp. before and after a single application of biolarvicides in Sululu and Igumbiro villages, south-eastern Tanzania. A previous study (Matowo et al., 2019) identified that Culex spp. mainly consisted of Cx. pipiens pipiens and Cx. quinquefasciatus.