Impact of Cymbopogon flexuosus (Poaceae) essential oil and primary components on the eclosion and larval development of Aedes aegypti.

The current study describes the effects of sub-lethal concentrations and constituent compounds (citral and geranyl acetate) of Cymbopogon flexuosus essential oil (EO) on the development of Aedes aegypti. We treated eggs with 6, 18, or 30 mg L-1 and larvae with 3 or 6 mg L-1 of EO and its major compounds (citral and geranyl acetate). Citral and geranyl acetate were evaluated at 18, 30, and 42 mg L-1 and compared with commercial growth inhibitors (diflubenzuron and methoprene). We measured larval head diameter, siphon length, and larval length. Finally, we examined concentrations of molt hormone (MH) and juvenile hormone III (JH III) using high-performance liquid chromatography coupled to mass spectrometry. All geranyl acetate concentrations decreased egg hatching, while EO altered molting among larval instars and between larvae and pupae, with an increase in the larval length (3 mg L-1: 6 ± 0.0 mm; 6 mg L-1: 6 ± 0.7 mm) and head width (3 mg L-1: 0.8 ± 0 mm; 6 mg L-1: 0.8 ± 0.0 mm) compared with the control group. We did not detect chromatographic signals of MH and JH III in larvae treated with C. flexuosus EO or their major compounds. The sub-lethal concentrations C. flexuosus EO caused a similar effect to diflubenzuron, namely decreased hormone concentrations, an extended larval period, and death.

Design of a Repellent Against Aedes aegypti (Diptera: Culicidae) Using in silico Simulations With AaegOBP1 Protein.

Skin irritation has been reported to be the main adverse effect of excessive use of N,N-diethyl-m-toluamide (DEET) and ethyl 3-acetyl(butyl)amino (IR3535) commercial repellents. Therefore, there is an interest in alternatives of natural origin such as essential oils (EOs) and major compounds, which have repellent effects but have no contraindications. The main purpose of the present study was to identify the repellent effect of selected terpenes on Aedes aegypti Linnaeus, 1762 (Diptera: Culicidae) by in silico analysis based on their affinity with the odorant protein AaegOBP1. The protein-metabolite interactions in 20 terpenes were analyzed using the SwissDock tool. Terpenes presenting the highest affinity compared with commercial repellents were selected to evaluate repellent activity at concentrations 0.1, 10, and 25% against Ae. aegypti. Different periods (0-2, 2-15, 15-60 min) were evaluated with DEET as a positive control. The toxicity of terpenes was verified through Osiris and Molinspiration Cheminformatics Software, and cytotoxicity assays in Vero and HepaRG cells were performed using the MTT method. Two formulations were prepared with polyethylene glycol to evaluate skin long-lasting in vivo assay. The results showed four terpenes: geranyl acetate, nerolidol, α-bisabolol, and nerol, with affinity to AaegOBP1 comparable with DEET and IR3535. Geranyl acetate, nerolidol, and their mixtures showed no cytotoxicity and protection percentages close to 100% during the test at concentrations 10 and 25%. Long-lasting assays with geranyl acetate and nerolidol formulate showed 3 h as maximum protection time with 100% protection percentage. These metabolites and their mixtures are candidates to repellent formulations with times and protection percentages similar to DEET.

Mitochondrial affectation, DNA damage and AChE inhibition induced by Salvia officinalis essential oil on Aedes aegypti larvae.

The aim of this research study was to understand the mechanism of action of Salvia officinalis (Lamiaceae) essential oil (EO) on Aedes aegypti larvae. We evaluated the effect on DNA damage, acetylcholinesterase (AChE) inhibition and mitochondrial enzymatic alterations. The major components were analyzed in silico using OSIRIS and Molispiration free software. Aedes aegypti DNA was extracted from mosquito larvae between third (L3) and fourth (L4) instars to determine the DNA fragmentation or degradation at S. officinalis EO lethal concentrations (LC10, LC20, LC50, and LC90). DNA integrity was assessed in both LCs in larvae treated for 24 h and in larvae homogenized with EO; we also assessed purified DNA larvae by a densitometric analysis. The AChE inhibition was quantified in protein larvae L3-L4 following Ellman's method and the enzymatic activities related to the mitochondrial respiratory chain of mitochondrial proteins was estimated by spectrophotometry. In silico analysis of 1,8-cineol and of α-thujone, major EO components, showed that they were highly permeable in biological membranes without mutagenic risks. Alterations in the integrity of DNA were observed in larvae exposed and homogenized with S. officinalis EO. The EO induced an AChE inhibition of 37 ±â€¯2.6% to IC50. On the other hand, mitochondrial bioenergetics suggest that EO inhibits electrons entry to the respiratory chain, via Complex II. AChE activity alteration causes mortality of individuals, by blocking the insect cholinergic functions. These results indicate that EO affects the integrity of DNA, the mitochondrial respiration chain and the AChE activity.