Effect of water source and feed regime on development and phenotypic quality in Anopheles gambiae (s.l.): prospects for improved mass-rearing techniques towards release programmes

Nwamaka O Akpodiete,Frédéric Tripet,Abdoulaye Diabate

doi:10.1186/s13071-019-3465-0

Nwamaka O Akpodiete, Frédéric Tripet + Show 1 more

Open Access

https://doi.org/10.1186/s13071-019-3465-0

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Abstract

BackgroundIn many malaria-endemic sub-Saharan countries, insecticide resistance poses a threat to existing mosquito control measures, underscoring the need for complementary control methods such as sterile and/or genetically-modified mosquito release programmes. The sibling species Anopheles gambiae and An. coluzzii are responsible for malaria transmission in most of this region. In their natural habitat, these species generally breed in clean, soft water and it is believed that divergent preference in their larval breeding sites have played a role in their speciation process. Mosquito release programmes rely on the rearing of mosquitoes at high larval densities. Current rearing protocols often make use of deionised water regardless of the strain reared. They also depend on a delicate balance between the need for adequate feeding and the negative effect of toxic ammonia and food waste build-up on mosquito development, making managing and improving water quality in the insectary imperative.MethodsHere, we investigated the impact of water source and feed regimes on emergence rate and phenotypic quality of mosquitoes in the insectary. First-instar larvae of An. gambiae (Kisumu strain) and An. coluzzii (Mopti and VK3 strains) were reared in three water sources with varying degrees of hardness (deionised, mineral and a mix of the two), with a daily water change. Larvae were fed daily using two standardised feeding regimes, solution and powder feed.ResultsWater source had a significant impact on mosquito size and development time for all strains. Earlier emergence of significantly larger mosquitoes was observed in mineral water with the smallest mosquitoes developing later from deionised water. Wing-length was significantly longer in mineral, mixed water and in powder feed, irrespective of sex, strains or water types. Deionised water was the least favourable for mosquito quality across all strains.ConclusionsMineral water and powder feed should be used in rearing protocols to improve mosquito quality where the optimal quality of mosquitoes is desired. Although results obtained were not significant for improved mosquito numbers, the phenotypic quality of mosquitoes reared was significantly improved in mineral water and mix water. Further studies are recommended on the impact mineral water has on other fitness traits such as longevity, fecundity and mating competitiveness.

Highlights

In many malaria-endemic sub-Saharan countries, insecticide resistance poses a threat to existing mosquito control measures, underscoring the need for complementary control methods such as sterile and/ or genetically-modified mosquito release programmes
A full logistic regression model showed that water source had a small but significant positive effect on larval survival across all strains (P = 0.0405) but that its impact differed between strains (P = 0.0117) (Table 4)
The same analyses performed within strains showed that water source improved larval survival for Kisumu and VK3 strains but not Mopti (Fig. 1, Additional file 1: Table S1)

Summary

Introduction

In many malaria-endemic sub-Saharan countries, insecticide resistance poses a threat to existing mosquito control measures, underscoring the need for complementary control methods such as sterile and/ or genetically-modified mosquito release programmes. The sibling species Anopheles gambiae and An. coluzzii are responsible for malaria transmission in most of this region. In sub-Saharan Africa, malaria is primarily transmitted by mosquitoes of the Anopheles gambiae complex with Anopheles gambiae and Anopheles coluzzii being the most abundant and widespread [3] These morphologically indistinguishable sibling species co-occur over large areas of sub-Saharan Africa and do not exhibit intrinsic post-mating barriers to reproduction [4]. Anopheles coluzzii has a westerly distribution which spans from Northern Senegal (West Africa), West-central Africa and Angola (Southern Africa) [5] In many of these regions, the two species are found in sympatry and are separated genetically by strong assortative mating, low hybridization rates [6, 7]. The second exception is populations in which the kdrresistance allele of An. gambiae recently selectively introgressed into An. coluzzii which resulted in a temporary increase in hybrid-like genotypes [9, 10]

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