Green tea proanthocyanidins cause impairment of hormone-regulated larval development and reproductive fitness via repression of juvenile hormone acid methyltransferase, insulin-like peptide and cytochrome P450 genes in Anopheles gambiae sensu stricto.

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

Prospects for malaria control through manipulation of mosquito larval habitats and olfactory-mediated behavioural responses using plant-derived compounds

Abstract Malaria presents an overwhelming public health challenge, particularly in sub-Saharan Africa where vector favourable conditions and poverty prevail, potentiating the disease burden. Behavioural variability of malaria vectors poses a great challenge to existing vector control programmes with insecticide resistance already acquired to nearly all available chemical compounds. Thus, approaches incorporating plant-derived compounds to manipulate semiochemical-mediated behaviours through disruption of mosquito olfactory sensory system have considerably gained interests to interrupt malaria transmission cycle. The combination of push-pull methods and larval control have the potential to reduce malaria vector populations, thus minimising the risk of contracting malaria especially in resource-constrained communities where access to synthetic insecticides is a challenge. In this review, we have compiled information regarding the current status of knowledge on manipulation of larval ecology and chemical-mediated behaviour of adult mosquitoes with plant-derived compounds for controlling mosquito populations. Further, an update on the current advancements in technologies to improve longevity and efficiency of these compounds for field applications has been provided

Effects of proanthocyanidin-rich fractions on survival of <i>An</i>. <i>gambiae</i> (<i>s</i>.<i>s</i>) larvae.

<p><b>(a)</b>: Dose-response curves showing acute toxicity effect of PA-rich fractions on L3/L4 instars. L3/L4 instars were exposed to various doses of PA-rich fractions and mortality rates recorded every 24 h until 48 h post-exposure. Half-maximal lethal concentration (LC₅₀) was established at 5.52 ppm for 24 h and 4.45 ppm for 48 h. <b>(b)</b>: Survival rates of L3/L4 instars on exposure to sublethal doses of PA-rich fractions relative to controls. Exposure of L3/L4 instars to sublethal doses of PA-rich fractions revealed dose-dependent survival rates with high survival rates exhibited in 1 ppm followed by 2.5 ppm, negative controls and least 5 ppm. Experimental data were collected from 3 independent replicates.</p

RT-qPCR gene-specific primer sets.

<p>The primers target genes for signal transduction, stress response, xenobiotic metabolism, JH biosynthesis, vitellogenesis and endogenous reference genes ribosomal s7 protein, α-tubulin.</p

Phenotypic aberrations exerted by proanthocyanidin-rich fractions on <i>An</i>. <i>gambiae</i> (<i>s</i>.<i>s</i>.) larval development.

<p>Exposure to green tea proanthocyanidin-rich fractions at sublethal doses disrupted larval development inducing abnormal larval-pupal intermediates and prevented adult emergence with mouthparts, wings and legs stuck within the pupal caste. <b>a</b>: Normal larvae, <b>b</b>: Normal larval-pupal intermediate, <b>c</b>: Abnormal larval-pupal intermediate, <b>d</b>: Disrupted adult emergence with mouthparts, wings and legs stuck within pupal exuvium, <b>e:</b> Failure in adult emergence showing legs stuck in pupal caste. Analysis was performed under a light microscope at magnification of 25×.</p

Sublethal dose effects of proanthocyanidin-rich fractions from <i>Camellia sinensis</i> leaf extract on development of <i>An</i>. <i>gambiae</i> (<i>s</i>.<i>s</i>.) mosquitoes.

<p>Sublethal dose effects of proanthocyanidin-rich fractions from <i>Camellia sinensis</i> leaf extract on development of <i>An</i>. <i>gambiae</i> (<i>s</i>.<i>s</i>.) mosquitoes.</p