The effect of silencing immunity related genes on longevity in the naturally occurring Anopheles arabiensis mosquito population of Southwest Ethiopia

Abstract

BackgroundIn the fight against malaria, vector control remains the most important tool, butit is now severely constrained by the spread of insecticide or behavioral resistance by mosquito populations. Therefore, new vector control tools are warranted. Such novel tools include anti-mosquito vaccines or mosquito genetic modifications targeting the mosquito midgut homeostasis and reducing the mosquito lifespan beyond a stage they can transmit malaria.\n\nMethodsWe assessed the effect of RNA interference silencing of the midgut homeostasis regulators FN3D1, FN3D2, FN3D3, GPRGR9 and PGRPLC3 in populations of Anopheles arabiensis reared at nearly natural setting. We monitored the survival of gene-silenced mosquitoes and assessed the load of their midgut microbiota using flow cytometry. The effect of gene silencing was modeled by the Cox proportional hazards frailty model, and bacterial counts were first log transformed and then compared by a mixed model.\n\nResultSignificantly higher mortality rates were observed for the FN3D1 (Hazard ratio =1.64, P=0.004), FN3D3 (HR=1.79, P<0.001) and GPRGr9 silenced mosquitoes (HR=2.00, P<0.001) as compared to a control group injected with dsRNA against a non-related bacterial gene LacZ. The bacterial load ratios for all target gene silenced mosquitoes compared to control mosquitoes were above 1, with the highest value for FN3D1 equal to 2.66 (95%CI: [0.94;7.57]) but no statistically significant difference could be demonstrated. Interestingly, there was a strong correlation (r=0.61) between the mortality hazard ratio and the bacterial count ratio of the gene-silenced mosquitoes. Increased mortality rates were reversed when the gene-silenced mosquitoes were treated with antibiotic mixtures suggesting that gut microbiota play a key role in the observed reduction of mosquito survival.\n\nConclusionWe demonstrate that interfering with the expression of theFN3D1, FN3D3 or GPRGr9 genes can cause a significant reduction of the longevity of An. arabiensis mosquitoes due to the disruption of the mosquito gut homeostasis.