Abstract
BackgroundMany studies have shown that the environment in which larvae develop can influence adult characteristics with consequences for the transmission of pathogens. We investigated how two environmental stresses (larviciding and nutritional stress) interact to affect Anopheles gambiae (previously An. gambiae S molecular form) life history traits and its susceptibility for field isolates of its natural malaria agent Plasmodium falciparum.MethodsLarvae were reared in the presence or not of a sub-lethal concentration of larvicide and under a high and low food regimen. Development time, individual size, adult survival and competence for P. falciparum were assessed.ResultsIndividuals under low food regimen took more time to develop, had a lower development success and were smaller while there was no main effect of larvicide exposure on these traits. However, larvicide exposure impacted individual size in interaction with nutritional stress. Female survival was affected by the interaction between gametocytemia, parasite exposure and larval diet, as well as the interaction between gametocytemia, parasite exposure and larvicidal stress, and the interaction between gametocytemia, larvicidal exposure and larval diet. Among the 951 females dissected 7 days post-infection, 559 (58.78 %) harboured parasites. Parasite prevalence was significantly affected by the interaction between larvicidal stress and larval diet. Indeed, females under low food regimen had a higher prevalence than females under high food regimen and this difference was greater under larvicidal stress. The two stresses did not impact parasite intensity.ConclusionsWe found that larval nutritional and larvicidal stresses affect mosquito life history traits in complex ways, which could greatly affect P. falciparum transmission. Further studies combining field-based trials on larvicide use and mosquito experimental infections would give a more accurate understanding of the effects of this vector control tool on malaria transmission.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1514-5) contains supplementary material, which is available to authorized users.
Highlights
Many studies have shown that the environment in which larvae develop can influence adult characteristics with consequences for the transmission of pathogens
Lethal concentrations The LC50 and LC90 were 0.23 mg/l (95 % confidence interval (CI) = 0.2–0.26) and 0.52 mg/l, respectively, for larvae exposed to high food quantities
Wing size The mosquitoes exposed to the low food treatment as larvae were significantly smaller than were their high food counterparts (3.6 ± 0.007 vs 4.1 ± 0.008 mm; χ2 = 2286, df = 1, P < 0.0001)
Summary
Many studies have shown that the environment in which larvae develop can influence adult characteristics with consequences for the transmission of pathogens. Current malaria vector control mostly relies on two main components: long-lasting insecticide treated bed nets and indoor residual spraying. They target only the adult stage, and individuals exhibiting endophilous and endophagous behaviours. Bti has shown promising results against many mosquito vectors [12,13,14,15,16,17,18] While this kind of bio-pesticide is unlikely to pose any hazard to humans, its efficacy depends on regular application due to a short residual activity. Bti efficacy may be difficult to maintain because Bti is sensitive to environmental characteristics such as vegetation and sun exposure, and breeding sites where applications are desired but may be difficult to identify [10]
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