Potential of Camellia sinensis proanthocyanidins-rich fraction for controlling malaria mosquito populations through disruption of larval development

Abstract

Background: Anopheles arabiensis and A. gambiae (sensu stricto) are the most prolific Afrotropical malaria vectors. Population control efforts of these two vectors have been hampered by extremely diverse larval breeding sites and widespread resistance to currently available insecticides. Control of mosquito larval stages using bioactive compounds of plant origin has the potential to suppress vector populations leading to concomitant reduction in disease transmission rates. In this study, we evaluated the efficacy of Camellia sinensis crude leaf extract and its fraction against the larvae of A. arabiensis and A. gambiae (s.s.).

Methods: Late third/early fourth instar larvae (L3/L4) of A. arabiensis and A. gambiae (s.s.) were exposed to increasing doses of C. sinensis leaf extract and its active fraction for 72 h, with mortality rates recorded every 24 h in both control and test groups. Ultra performance liquid chromatography electron spray ionization quadruple time of flight coupled with mass spectrometry (UPLC/ESI-Qtof/MS) was used to determine the main active constituents in the fraction.

Results: The major bioactive chemical constituents in the C. sinensis leaf extract were identified to be proanthocyanidins. The extract significantly interfered with larval survival and adult emergence in both species (ANOVA, F _(5,24) = 1435.92, P < 0.001). Additionally, larval exposure to crude extract at 250 ppm and 500 ppm for 24 h resulted in larval mortality rates of over 90 % in A. gambiae (s.s.) and 75 % in A. arabiensis. A relatively lower concentration of 100 ppm resulted in moderate mortality rates of < 50 % in both species, but induced growth disruption effects evident as abnormal larval-pupal intermediates and disrupted adult emergence. The estimated LC₅₀ concentrations of the crude leaf extract against A. arabiensis and A. gambiae (s.s.) larvae at 24 h were 154.58 ppm (95 % CI: 152.37-158.22) and 117.15 ppm (95 % CI: 112.86-127.04), respectively. The bioactive polar fraction caused 100 % larval mortality in both vector species at 25 ppm.

Conclusions: Our findings demonstrate the potential of green tea extract and its active constituents in disrupting mosquito larval development. This could contribute to the control of mosquito populations and improved management of malaria.

Keywords: Anopheles arabiensis; Anopheles gambiae (sensu stricto); Camellia sinensis; Larvicidal activity; Proanthocyanidins; Vector control.

Fig. 1

UPLC/ESI-Qtof/MS analysis profile of bioactive fraction of Camellia sinensis leaf extract. Six bioactive compounds were detected as follows: 2-Caffeine, 3-Quercetin, 4-Kaempferol, 5-Kaempferol rhamnoside, 6-Kaempferol rhamnosyl glucoside, 8-Proanthocyanidin. Proanthocyanidin m/z 593.2830 was the most abundant compound (15.2641 %)

Fig. 2

Dose-response curves showing treatment effects of bioactive fraction of C. sinensis on A. arabiensis and A. gambiae (s.s.) larvae at 24, 48 and 72 h post-exposure. Doses of the extract are log-transformed. The curves show dose-response fitted models of A. arabiensis (a) and A. gambiae (s.s.) (b) larvae, treated with bioactive fraction of C. sinensis at different exposure time periods (24, 48 and 72 h). Each point on the curve represents percentage mean (± standard deviation, SD) larval mortality of five replicates for a particular dose

Fig. 3

Growth disruption effects mediated by Camellia sinensis extract at 72 h post-exposure. a Anopheles gambiae (s.s.) control larva. b Anopheles arabiensis control larva. c Abnormal A. gambiae (s.s.) larval-pupal intermediate. d Abnormal An. arabiensis larval-pupal intermediate. e Aborted adult emergence in A. gambiae (s.s.) with legs stuck in pupal caste. f An. arabiensis adult emergence arrested (visualization of the changes in larval morphology before and after treatment with extract was monitored using light microscopy at 25× magnification)