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. 2024 Jan 10;14(1):1002.
doi: 10.1038/s41598-024-51152-1.

Influence of larval growth and habitat shading on retreatment frequencies of biolarvicides against malaria vectors

Betwel J Msugupakulya  1   2 , Swedi K Ngajuma  3 , Athuman N Ngayambwa  3 , Baraka E Kidwanga  3 , Ibrahim R Mpasuka  3 , Prashanth Selvaraj  4   5 , Anne L Wilson #  6 , Fredros O Okumu #  3   5   7   8
Affiliations

Influence of larval growth and habitat shading on retreatment frequencies of biolarvicides against malaria vectors

Betwel J Msugupakulya et al. Sci Rep. .

Abstract

Effective larviciding for malaria control requires detailed studies of larvicide efficacies, aquatic habitat characteristics, and life history traits of target vectors. Mosquitoes with brief larval phases present narrower timeframes for biolarvicidal effects than mosquitoes with extended periods. We evaluated two biolarvicides, VectoBac (Bacillus thuringiensis israelensis (Bti)) and VectoMax (Bti and Bacillus sphaericus) against Anopheles funestus and Anopheles arabiensis in shaded and unshaded habitats; and explored how larval development might influence retreatment intervals. These tests were done in semi-natural habitats using field-collected larvae, with untreated habitats as controls. Additionally, larval development was assessed in semi-natural and natural habitats in rural Tanzania, by sampling daily and recording larval developmental stages. Both biolarvicides reduced larval densities of both species by >98% within 72 h. Efficacy lasted one week in sun-exposed habitats but remained >50% for two weeks in shaded habitats. An. funestus spent up to two weeks before pupating (13.2(10.4-16.0) days in semi-natural; 10.0(6.6-13.5) in natural habitats), while An. arabiensis required slightly over one week (8.2 (5.8-10.6) days in semi-natural; 8.3 (5.0-11.6) in natural habitats). The findings suggest that weekly larviciding, which is essential for An. arabiensis might be more effective for An. funestus whose prolonged aquatic growth allows for repeated exposures. Additionally, the longer residual effect of biolarvicides in shaded habitats indicates they may require less frequent treatments compared to sun-exposed areas.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Dynamics of larvae and larval period of An. funestus and An. arabiensis in the natural habitats.
Figure 2
Figure 2
Larval period of An. funestus and An. arabiensis in the semi-natural habitats.
Figure 3
Figure 3
Semi-natural habitats created at Mosquito City (a). The habitats were created either outside the semi-field screen houses, i.e., open to direct sunlight (b), or inside the semi-field systems, i.e., shaded environment (c). (d) An aquatic habitat with the netting cover removed.
Figure 4
Figure 4
Study sites for the efficacy of the biolarvicides, collection of larvae and adult mosquitoes, and observations of larval periods in natural habitats.
See this image and copyright information in PMC

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