Laboratory and simulated semi-field larvicidal efficacy of Aframomum angustifolium (Sonn.) K. Schum and Tagetes patula essential oils against Anopheles gambiae

Abstract

Introduction: Malaria is a vector-borne, important public health problem spread by mosquitoes in tropical regions. The use of synthetic insecticides for mosquito control has been linked to insecticide resistance and environmental consequences. Thus, there is an urgent need to search for new highly selective and biodegradable insecticides lacking long-term toxicity to humans and mammals which are botanical-based compounds from indigenous plant sources available in local communities. Therefore, this study focused on evaluating the larvicidal activity of Aframomum angustifolium and Tagetes patula essential oils against Anopheles gambiae larvae in laboratory and simulated fields. Methods: The Eos was extracted by the hydro distillation method, and the chemical composition of the Eos was determined using gas chromatography-mass spectrometry (GC-MS). The WHO protocol was followed for the laboratory and the simulated bioassays. Both laboratory-reared and field-collected larvae, as well as non-targeted organisms (Gambusia affinis), were used in simulated field conditions. The collected data were analyzed using probit analysis, and their means were compared in one-way analysis of variance (ANOVA) using IBM SPSS Statistic version 26. Results: The main active ingredients in T. patula Eo were terpinolene (20.75 %) and (Z)-ocimene (17.10 %) and A. angustifolium were cis-pinen-3-ol (58.48 %) β-pinene (31.03 %). The EO of T. patula was the most efficacious in the bioassay. The larvicidal bioassay findings demonstrated that the mortality rate was dose- and exposure- dependent. In the laboratory, the EOs of A. angustifolium and T. patula have larvicidal activity against An. gambiae larvae, with LC50 values of 1.71 and 0.71 ppm after 48 h, respectively. Both binary combinations of the EOs showed synergistic interactions at 24 h but antagonistic interactions at 48 h. In the simulated field trial using laboratory-reared larvae, the mortality rate was higher in the simulated setting compared with the laboratory setting for all the tested concentrations for both EOs. Only A. angustifolium EO was toxic against Gambusia affins at 100 ppm. Conclusion: The findings of this study have shown that T. patula and A. angustifolium oils have good larvicidal activities for An. gambiae. The two plants are potential sources of larvicidal compounds that could be used to control the malaria vector.