Natasha Agramonte

The oregano, Origanum onites L., essential oil (EO) was tested in laboratory behavioural bioassays for repellent activity against Amblyomma americanum (L.) and Aedes aegypti (L.). The O. onites EO was characterised using GC-FID and GC-MS. Carvacrol (75.70%), linalool (9.0%), p-cymene (4.33%) and thymol (1.9%) were the most abundant compounds. At a concentration of 0.413 mg oil/cm(2) of filter paper, O. onites EO repelled 100% of the ticks tested and at 0.103 mg oil/cm(2) of filter paper, 66.7% of the ticks were repelled. At 0.075 mg oil/cm(2) filter paper, thymol repelled 66.7% of the ticks compared to 28.7% by carvacrol at that same concentration. Against Ae. aegypti, O. onites EO was repellent at the minimum effective dosage (MED) of 0.011 (±0.00) mg/cm(2) in the cloth patch assay compared to the reference control, N,N-dimethyl-3-methylbenzamide (DEET) with a MED = 0.007 ± (0.003) mg/cm(2).

Repellents prevent mosquito bites and help reduce mosquito-borne disease, a global public health issue. Laboratory-based repellent bioassays predict the ability of compounds to deter mosquito feeding, but the variety of repellent bioassays and statistical analysis methods makes it difficult to compare results across methodologies. The most realistic data are collected when repellents are applied on the skin; however, this method exposes volunteers to chemicals and mosquito bites. Silicone membranes were investigated as an alternative to human skin in assays of repellent efficacy. Results from module system bioassays conducted in vitro with a silicone membrane were compared with in vivo bioassays conducted with N,N-diethyl-3-methylbenzamide (referred to as DEET), 1-piperidinecarboxylic acid 2-(2-hydroxyethyl)-1-methylpropylester (referred to as Picaridin), ethyl 3-[acetyl(butyl)amino]propanoate (referred to as IR3535), and para-menthane-3,8-diol (referred to as PMD) applied directly ...

The essential oil (EO) of the aerial parts of Rhanterium epapposum Oliv. (Asteraceae), was obtained by hydrodistillation. The oil was subsequently analyzed by both GC-FID and GC-MS, simultaneously. Forty-five components representing 99.2% of the oil composition were identified. The most abundant compounds were camphene (38.5%), myrcene (17.5%), limonene (10.1%) and α-pinene (8.7%). Referring to the ethnobotanical utilization, an insecticidal assay was performed, where the oil repelled the yellow fever mosquito Aedes aegypti L. at a minimum effective dose (MED of 0.035 ± 0.010 mg/cm(2)) compared to the positive control DEET (MED of 0.015 ± 0.004 mg/cm(2)). Additionally, the in vitro antimicrobial activity against a panel of pathogens was determined using a microdilution method. The acetyl- and butyrylcholine esterase inhibitory activities were measured using the colorimetric Ellman method. The bioassay results showed that the oil was rather moderate in antimicrobial and cholinesterase inhibitions when compared to the standard compounds.

The essential oils from the flower, leaf, and stem of Echinophora lamondiana B.Yildiz et Z.Bahcecioglu were analyzed by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry. In total, 41, 37, and 44 compounds were identified, which accounted for 98.0, 99.1, and 97.0% of flower, leaf, and stem essential oils, respectively. The monoterpenic hydrocarbons were found to be high in all samples of the essential oils. The major components of essential oils from flower, leaf, and stem of E. lamondiana were δ-3-carene (61.9, 75.0, and 65.9%, respectively), α-phellandrene (20.3, 14.1, and 12.8%, respectively), and terpinolene (2.7, 3.3, and 2.9%, respectively). Flower and leaf essential oils and terpinolene produced biting deterrence similar to 25 nmol/cm(2) N, N-diethyl-meta-toluamide (DEET; 97%) against Aedes aegypti (L.) and Anopheles quadrimaculatus Say. Compounds (+)-δ-3-carene, (R)-(-)-α-phellandrene, and water-distilled essential oils were significantly less repellent than DEET. Among essential oils, leaf oil was the least toxic of the oils, with an LC50 value of 138.3 ppm, whereas flower essential oil killed only 32% larvae, and no mortality of stem oil at highest tested dosages against Ae aegypti was observed. Terpinolene and α-phellandrene showed higher toxicity than δ-3-carene in both the species. In contrast to Ae. aegypti, all the essential oils showed toxicity in An. quadrimaculatus, and toxicity was higher in leaf oil than the other two oils. These results could be useful in finding new, safe, and more effective natural biopesticides and biting deterrent or repellents against Ae. aegypti.

In this study we evaluated the biting deterrent effects of a series of saturated and unsaturated fatty acids against Aedes aegypti (L), yellow fever mosquito (Diptera: Culicidae) using the K & Dbioassay module system. Saturated (C6:0 to C16:0 and C18:0) and unsaturated fatty acids (C11:1 to C14:1, C16:1, C18:1, and C18:2) showed biting deterrence index (BDI) values significantly greater than ethanol, the negative control. Among the saturated fatty acids, mid chain length acids (C10:0 to C13:0) showed higher biting deterrence than short (C6:0 to C9:0) and long chain length acids (C14:0 to C18:0), except for C8:0 and C16:0 that were more active than the other short and long chain acids. The BDI values of mid chain length acids (C10:0 to C13:0) were not significantly less than N, N-diethyl-meta-toluamide (DEET), the positive control. Among the unsaturated fatty acids, C11:1 showed the highest activity (BDI = 1.05) and C18:2 had the lowest activity (BDI = 0.7). In C11:1, C12:1, and C14:...