Abstract
Successful optimization of plant-derived compounds into control of nuisance insects would benefit from scientifically validated targets. However, the close association between the genotypic responses and physiological toxicity effects mediated by these compounds remains underexplored. In this study, we evaluated the sublethal dose effects of proanthocyanidins (PAs) sourced from green tea (Camellia sinensis) on life history traits of Anopheles gambiae (sensu stricto) mosquitoes with an aim to unravel the probable molecular targets. Based on the induced phenotypic effects, genes selected for study targeted juvenile hormone (JH) biosynthesis, signal transduction, oxidative stress response and xenobiotic detoxification in addition to vitellogenesis in females. Our findings suggest that chronic exposure of larval stages (L3/L4) to sublethal dose of 5 ppm dramatically extended larval developmental period for up to 12 days, slowed down pupation rates, induced abnormal larval-pupal intermediates and caused 100% inhibition of adult emergence. Further, females exhibited significant interference of fecundity and egg hatchability relative to controls (p < 0.001). Using reverse transcription quantitative polymerase chain reaction (RT-qPCR), our findings show that PA-treated larvae exhibited significant repression of AgamJHAMT (p < 0.001), AgamILP1 (p < 0.001) and AgamCYP6M2 (p < 0.001) with up-regulation of Hsp70 (p < 0.001). Females exposed as larvae demonstrated down-regulation of AgamVg (p = 0.03), AgamILP1 (p = 0.009), AgamCYP6M2 (p = 0.05) and AgamJHAMT (p = 0.02). Our findings support that C. sinensis proanthocyanidins affect important vectorial capacity components such as mosquito survival rates and reproductive fitness thus could be potentially used for controlling populations of malaria vectors.
Highlights
The mosquito Anopheles gambiae is the most dynamically evolving and efficient malaria vector in sub-Saharan Africa [1,2,3]
Our findings show that the PA-rich fraction of C. sinensis leaf extracts dramatically protracted the larval developmental period, disrupted adult emergence, and remarkably reduced female fecundity and egg hatchability
We investigated the effects of sublethal concentrations of C. sinensis PA-rich fraction, which previously demonstrated larvicidal and growth disruption activities against malaria vectors [54], on An. gambiae (s.s.) larval development and reproductive fitness
Summary
The mosquito Anopheles gambiae (sensu stricto) is the most dynamically evolving and efficient malaria vector in sub-Saharan Africa [1,2,3]. Reduction of vectorial capacity below the critical threshold required to achieve a basic reproduction rate of less than 1 is the ultimate goal of vector control interventions [7]. Efforts to control these devastating disease-transmitting vectors using chemical insecticides have reduced global malaria incidences by 37% and 42% in Africa [8]. Interventions targeting the immature stages of mosquitoes that are susceptible to chemical attacks and with limited chances of developing resistance seem quite promising vector control approaches that could reduce malaria transmission rates in high transmission endemic regions [10, 11]. Several studies have shown direct consequential impacts of manipulative effect of larval ecology on life history attributes and capacity of emergent mosquitoes to transmit Plasmodium falciparum parasites [12,13,14,15]
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