Abstract
BackgroundThe origin of highly competent malaria vectors has been linked to productive larval habitats in the field, but there isn't solid quantitative or qualitative data to support it. To test this, the effect of larval habitat soil substrates on larval development time, pupation rates and vector competence of Anopheles gambiae to Plasmodium falciparum were examined.MethodsSoils were collected from active larval habitats with sandy and clay substrates from field sites and their total organic matter estimated. An. gambiae larvae were reared on these soil substrates and the larval development time and pupation rates monitored. The emerging adult mosquitoes were then artificially fed blood with infectious P. falciparum gametocytes from human volunteers and their midguts examined for oocyst infection after seven days. The wing sizes of the mosquitoes were also measured. The effect of autoclaving the soil substrates was also evaluated.ResultsThe total organic matter was significantly different between clay and sandy soils after autoclaving (P = 0.022). A generalized liner model (GLM) analysis identified habitat type (clay soil, sandy soil, or lake water) and autoclaving (that reduces presence of microbes) as significant factors affecting larval development time and oocyst infection intensities in adults. Autoclaving the soils resulted in the production of significantly smaller sized mosquitoes (P = 0.008). Autoclaving clay soils resulted in a significant reduction in Plasmodium falciparum oocyst intensities (P = 0.041) in clay soils (unautoclaved clay soils (4.28 ± 0.18 oocysts/midgut; autoclaved clay soils = 1.17 ± 0.55 oocysts/midgut) although no difference (P = 0.480) in infection rates was observed between clay soils (10.4%), sandy soils (5.3%) or lake water (7.9%).ConclusionThis study suggests an important nutritional role for organic matter and microbial fauna on mosquito fitness and vector competence. It shows that the quality of natural aquatic habitats of mosquito larvae may influence malaria parasite transmission potential by An. gambiae. This information can be important in targeting larval habitats for malaria control.
Highlights
The origin of highly competent malaria vectors has been linked to productive larval habitats in the field, but there isn't solid quantitative or qualitative data to support it
It shows that the quality of natural aquatic habitats of mosquito larvae may influence malaria parasite transmission potential by An. gambiae
It has been shown that nutritional resources in larval habitats determine adult mosquito size [3], and that a relationship exists between size and parasite infectivity [4], yet no studies have been conducted to determine if natural mosquito larval habitat substrates have an effect on mosquito productivity or Plasmodium falciparum parasite infectivity in the adult mosquitoes
Summary
The origin of highly competent malaria vectors has been linked to productive larval habitats in the field, but there isn't solid quantitative or qualitative data to support it. Malarial vectors in the Anopheles gambiae complex are known to use diverse small water bodies as larval habitats [1]. These habitats differ in physical as well as biological characteristics, which directly influence the distribution and abundance of larval mosquito populations in nature [2]. While it is known from laboratory studies that larval mosquito nutrition affects vector competence [3,4], the factors that determine adult An. gambiae fitness for malaria parasite transmission in the field are unclear, with only anecdotal evidence suggesting a role for larval habitat productivity [4]. The underlying influences of soil type and organic matter content on larval development, adult mosquito productivity and on the corresponding malaria parasite transmission potential of An. gambiae have not been given much attention
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