Methanolic Extracts of Chiococca alba in Aedes aegypti Biorational Management: Larvicidal and Repellent Potential, and Selectivity against Non-Target Organisms

Abstract

The use of formulations containing botanical products for controlling insects that vector human and animal diseases has increased in recent years. Plant extracts seem to offer fewer risks to the environment and to human health without reducing the application strategy's efficacy when compared to synthetic and conventional insecticides and repellents. Here, we evaluated the potential of extracts obtained from caninana, Chiococca alba (L.) Hitchc. (Rubiaceae), plants as a tool to be integrated into the management of Aedes aegypti, one of the principal vectors for the transmission of arborviruses in humans. We assessed the larvicidal and repellence performance against adult mosquitoes and evaluated the potential undesired effects of the extracts on non-target organisms. We assessed the susceptibility and predatory abilities of the nymphs of Belostoma anurum, a naturally occurring mosquito larva predator, and evaluated the C. alba extract's cytotoxic effects in mammalian cell lines. Our chromatographic analysis revealed 18 compounds, including rutin, naringin, myricetin, morin, and quercetin. The methanolic extracts of C. alba showed larvicidal (LC₅₀ = 82 (72-94) mg/mL) activity without killing or affecting the abilities of B. anurum to prey upon mosquito larvae. Our in silico predictions revealed the molecular interactions between rutin and the AeagOBP1 receptor to be one possible mechanism for the repellent potential recorded for formulations containing C. alba extracts. Low cytotoxicity against mammalian cell lines reinforces the selectivity of C. alba extracts. Collectively, our findings highlight the potential of C. alba and one of its constituents (rutin) as alternative tools to be integrated into the management of A. aegypti mosquitoes.

Keywords: alternative insecticides; botanical pesticides; caninana plants; molecular docking predictions.

Figure 1

HPLC fingerprint of the methanolic extract of Chiococca alba, detected at 280 nm. Peak 1: rutin; peak 2: naringin; peak 3: myricetin; peak 4: morin; peak 5: quercetin. Insert: HPLC chromatogram of the authentic standards of the phenolic compounds mixture.

Figure 2

Susceptibility of Aedes aegypti larvae (A) and Belostoma anurum nymphs (B) to methanolic extracts of Chiococca alba. (C) The number of A. aegypti larvae preyed upon by B. anurum nymphs over time, with and without a period (96 h) of recovery after exposure to the C. alba methanolic extract (200 µg/mL) (left). The total number of A. aegypti larvae preyed upon by B. anurum nymphs (right). The control treatment consisted of unexposed nymphs. (A) A filled circle indicates the mortality values obtained with the extract application, while dotted lines represent the 95% confidence intervals. (B) Data are the mean ± SE. (C) The predatory ability was assessed at the larval density of six larvae/100 mL of water. Larval densities were reestablished after every evaluation. Symbols show the average number of larvae preyed upon by each B. anurum nymph (n = 15). Data are the mean ± SE. * denotes significant differences in the total number of preyed larvae between the two exposure times (i.e., without recovery and after 72 h recovery).

Figure 3

Repellent activity of formulations containing the Chiococca alba methanolic extract (A) and rutin (B) against Aedes aegypti adult females. (C,D) The number of bites from A. aegypti females after the application of C. alba methanolic extract (C) and rutin (D) in different formulations on human volunteers’ forearms. The parameters of the nonlinear regressions are described in Supplementary Table S1.

Figure 4

Rutin binds to the Aedes aegypti odorant binding protein (AeagOBP1). (A) Docking view of rutin with the AeagOBP1 binding site. (B) The 2D maps demonstrate the molecular interactions with amino acids from the AeagOBP1active site and rutin.

Figure 5

Toxicity of the methanolic extract of Chiococca alba and rutin to the human monocyte, THP-1. (A) The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test after 48 h of cell exposure to the C. alba extracts, indicating cell death at concentrations of 0.85, 1.30, 1.70, and 2.12 μg/mL (P < 0.0001). (B) The MTT test after 48 h of cell exposure to the rutin, indicating cell death at concentrations of 1.30, 1.70, and 2.12 μg/mL (* Significant at p < 0.001).