Chemical composition and assessment of larvicidal and repellent capacity of 14 Lamiaceae essential oils against Aedes albopictus.

In the current laboratory study, 14 essential oils (EOs) derived from 12 Lamiaceae plant species and their major components were screened for their larvicidal and repellent properties against Aedes albopictus, an invasive mosquito species of great medical importance. The results of toxicity bioassays revealed that the EOs from Thymus vulgaris, Ocimum basilicum, Origanum dictamnus, Origanum majorana, and Origanum vulgare, as well as their major components (terpenes), namely thymol, carvacrol, p-cymene, and γ-terpinene exerted the highest larvicidal effect. Essential oils from Mellisa officinalis, Origanum dictamus, Mentha spicata (chem. piperitenone epoxide), Origanum majorana, and Satureja thymbra were the most potent repellents, with the last two assigned as the best ones. Among the terpenes tested, piperitenone epoxide, carvacrol, thymol, and piperitenone provided the highest level of protection against Ae. albopictus adults. Chemical analysis revealed the presence of a high number of terpenes in the EOs, while in most cases, the biological action of the tested EOs and their major components was in consistency. The most effective EOs and terpenes that were identified through the current laboratory bioassays could be used as alternative agents to control larvae and repel adults of Ae. albopictus.

Antimicrobial activity of essential oils of cultivated oregano (Origanum vulgare), sage (Salvia officinalis), and thyme (Thymus vulgaris) against clinical isolates of Escherichia coli, Klebsiella oxytoca, and Klebsiella pneumoniae.

BACKGROUND: Oregano (Origanum vulgare), sage (Salvia officinalis), and thyme (Thymus vulgaris) are aromatic plants with ornamental, culinary, and phytotherapeutic use all over the world. In Europe, they are traditionally used in the southern countries, particularly in the Mediterranean region. The antimicrobial activities of the essential oils (EOs) derived from those plants have captured the attention of scientists as they could be used as alternatives to the increasing resistance of traditional antibiotics against pathogen infections. Therefore, significant interest in the cultivation of various aromatic and medicinal plants is recorded during the last years. However, to gain a proper and marketable chemotype various factors during the cultivation should be considered as the geographical morphology, climatic, and farming conditions. In this frame, we have studied the antimicrobial efficiency of the EOs from oregano, sage, and thyme cultivated under different conditions in a region of NE Greece in comparison to the data available in literature. METHODS: Plants were purchased from a certified supplier, planted, and cultivated in an experimental field under different conditions and harvested after 9 months. EOs were extracted by using a Clevenger apparatus and tested for their antibacterial properties (Minimum inhibitory concentration - MIC) against clinical isolates of multidrug resistant Escherichia coli (n=27), Klebsiella oxytoca (n=7), and Klebsiella pneumoniae (n=16) strains by using the broth microdilution assay. RESULTS: Our results showed that the most sensitive organism was K. oxytoca with a mean value of MIC of 0.9 µg/mL for oregano EOs and 8.1 µg/mL for thyme. The second most sensitive strain was K. pneumoniae with mean MIC values of 9.5 µg/mL for thyme and 73.5 µg/mL for oregano EOs. E. coli strains were among the most resistant to EOs antimicrobial action as the observed MICs were 24.8-28.6 µg/mL for thyme and above 125 µg/mL for thyme and sage. Most efficient were the EOs from thyme followed by those of oregano. CONCLUSIONS: With MIC values above 150 µg/mL, sage EOs did not show any antibacterial efficiency against the majority of the strains. However, no significant differences were observed concerning the antimicrobial action of all EOs originating from irrigated versus non-irrigated cultivated aromatic plants.

Insecticidal activity of plant essential oils against the vine mealybug, Planococcus ficus.

The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), is a pest in grape vine growing areas worldwide. The essential oils from the following aromatic plants were tested for their insecticidal activity against P. ficus: peppermint, Mentha piperita L. (Lamiales: Lamiaceae), thyme-leaved savory, Satureja thymbra L., lavender, Lavandula angustifolia Mill, and basil, Ocimum basilicum L. Essential oils from peels of the following fruits were also tested: lemon, Citrus limon L. (Sapindales: Rutaceae), and orange, C. sinensis L. The reference product was paraffin oil. Bioassays were conducted in the laboratory by using spray applications on grape leaves bearing clusters of P. ficus of one size class, which mainly represented either 3rd instar nymphs or pre-ovipositing adult females. The LC50 values for each essential oil varied depending on the P. ficus life stage but did not significantly differ between 3(rd) instar nymphs and adult females. The LC50 values of the citrus, peppermint, and thyme-leaved savory essential oils ranged from 2.7 to 8.1 mg/mL, and the LC50 values of lavender and basil oil ranged from 19.8 to 22.5 and 44.1 to 46.8 mg/mL, respectively. The essential oils from citrus, peppermint and thymeleaved savory were more or equally toxic compared to the reference product, whereas the lavender and basil essential oils were less toxic than the paraffin oil. No phytotoxic symptoms were observed on grape leaves treated with the citrus essential oils, and low phytotoxicity was caused by the essential oils of lavender, thyme-leaved savory, and mint, whereas the highest phytotoxicity was observed when basil oil was used.

Bioactivity of Dianthus caryophyllus, Lepidium sativum, Pimpinella anisum, and Illicium verum essential oils and their major components against the West Nile vector Culex pipiens.

Mosquitoes constitute a severe health problem in many areas all over the world. There are many regions of the tropics and subtropics where mosquitoes are one of the main reasons for inhibiting the economic upgrade. Except nuisance, their medical importance is another matter of attention since mosquitoes are vectors for a wide variety of vector-borne diseases. Due to disadvantages of currently used chemical control methods, it is unavoidable to search for eco-friendly new molecules. We report herein the evaluation of the larvicidal effect exhibited by essential oils of Dianthus caryophyllus, Lepidium sativum, Pimpinella anisum, and Illicium verum against late third to early fourth instar mosquito larvae of Culex pipiens. Furthermore, phytochemical analysis of plant samples revealed their major compounds to be ß-caryophyllene, eugenol, eucalyptol, α-terpinyl acetate, and (E)-anethole which were also tested for their potential larvicidal activity. For D. caryophyllus and L. sativum, this was the first report on the chemical composition of their essential oils. The essential oils of I. verum and P. anisum demonstrated high larvicidal activity with a LC(50) <18 mg L(-1). The other two essential oils of D. caryophyllus and L. sativum revealed moderate larvicidal activity, displaying a LC(50) value above 50 mg L(-1). Among the pure components, the most toxic were eugenol, (E)-anethole, and α-terpinyl acetate, with LC(50) values 18.28, 16.56, and 23.03 mg L(-1), respectively. Eucalyptol (1,8 cineole) and ß-caryophyllene were inactive at concentrations even as high as 100 mg L(-1), showing the least significant activity against mosquito larvae. Results allow some rationalization on the relative importance of the major compounds regarding the larvicidal activity of selected essential oils and their potential use as vector control agents.

Evaluation of bioefficacy of three Citrus essential oils against the dengue vector Aedes albopictus (Diptera: Culicidae) in correlation to their components enantiomeric distribution.

Laboratory experiments were conducted to study the bioefficacy against Ae. albopictus of three Citrus essential oils, derived from peels of Citrus sinensis, Citrus limon, and Citrus paradise and of their components. Chiral gas chromatography analysis revealed the dominant occurrence of R-(+)-limonene and (-)-ß-pinene in all three essential oils while in the case of lemon oil γ-terpinene, neral, and geranial detected also among other components. The tested Citrus essential oils were toxic against mosquito larvae with LC(50) values ranging from 25.03 to 37.03 mg l(-1). Among citrus essential oils components tested, γ-terpinene was the most toxic (LC(50) = 20.21 mg l(-1)) followed by both enantiomeric forms of limonene (LC(50) = 35.99 and 34.89 mg l(-1), for R-(+)-limonene and S-(-)-limonene, respectively). The delayed toxic effects after exposure of larvae to sublethal (LC(50)) doses were also investigated for citrus essential oils and their major component R-(+)-limonene, indicating a significant reduction of pupal survival. In repellent bioassays, lemon essential oil, S-(-)-limonene, citral (mixture of neral\geranial) and (+)-ß-pinene were the most effective compared with other citrus essential oils and components against adult mosquitoes. Repellent bioassays also revealed that limonenes and ß-pinenes showed an isomer dependence repellent activity. Finally, according to enantiomeric distribution of limonene and α- and ß-pinene, the repellency of lemon essential oil is possibly attributed to the presence of citral.

Classification of Greek Mentha pulegium L. (Pennyroyal) samples, according to geographical location by Fourier transform infrared spectroscopy.

INTRODUCTION: Mentha pulegium L. (pennyroyal) is one of the four most commercially important Mentha species, even it is not a cultivated plant. It can be abundantly located in the Iberian Peninsula and North African countries. In Greece it grows in the wild and it is scattered all over the country. Pennyroyal is best known for its essential oil, with Spain and Morocco being the largest producers in the world. Mid-infrared spectroscopy has been applied to determine the origin of various samples. OBJECTIVES: In this work Fourier transform infrared spectroscopy (FT-IR) combined with canonical discriminant analysis has been applied to distinguish 70 Greek pennyroyal samples according to their collection areas. MATERIAL AND METHODS: Pennyroyal nonpolar organic extracts were prepared using ultrasound-assisted solvent extraction. The spectra of the extracts were recorded in the range of 4000-400 cm(-1) and the best discrimination was achieved in the spectral region 1720-1650 cm(-1) . RESULTS: Spectral features for the discrimination of pennyroyal samples among the different collection areas occur primarily in the carbonyl region and are correlated with the main volatile constituents of the extracts (menthone, isomenthone, pulegone, piperitone). All areas were easily differentiated by canonical discriminant analysis. The percentages of correct classification and validation were 94.3 and 90.0%, respectively. CONCLUSION: The combination of FT-IR spectroscopy and multivariate analysis provides a rapid and ambient method to discriminate pennyroyal samples in terms of geographical origin.

Quantitative determination of pulegone in pennyroyal oil by FT-IR spectroscopy.

Pulegone constitutes a monoterpene occurring in Mentha species and primarily in Mentha pulegium L. (pennyroyal). A major source of human exposure to pulegone is the use of pennyroyal essential oil in flavorings, confectionery and cosmetics. The rapid quantification of pulegone in hydrodistilled pennyroyal oils (which were also "spiked" to increase the validation range) by Fourier transform infrared spectroscopy (FT-IR) combined with partial least-squares (PLS) regression was evaluated, using the spectral region 1650-1260 cm(-1). Gas chromatography was applied as the reference method for pennyroyal oil samples, which ranged in pulegone content from 157 to 860 mg/mL. The two methods were subjected to statistical tests and proved equivalent in terms of accuracy and reproducibility (99% confidence level). The use of FT-IR spectroscopy could offer a viable alternative to the standard analysis procedures presently applied for quantification of valuable plant substances and could also provide the processing industry with a simple and high-throughput technique for the fast quality check of incoming raw materials such as pennyroyal oils.

Coactivity of sulfide ingredients: a new perspective of the larvicidal activity of garlic essential oil against mosquitoes.

BACKGROUND: The activity of several garlic oil ingredients against Culex pipiens L. larvae was studied. In addition to diallyl sulfide (DS) and diallyl disulfide (DDS), the garlic oils used included one essential oil (EO) and two semi-synthetic garlic essential oils (SSGEO1 and SSGEO2), which resulted from the enrichment of EO with DS and DDS standards respectively. The oils were compared with respect to their toxicity. RESULTS: The chemical composition of the tested oils was evaluated by means of gas chromatography-mass spectrometry. Experimental data from the tested samples revealed high toxicity. In detail, DDS (6.09 mg L(-1)) was the most active, followed by SSGEO2 (7.05 mg L(-1)) and EO (8.01 mg L(-1)), while SSGEO1 and DS were relatively inactive. CONCLUSION: The addition of DDS to EO did not change the toxic effect of the essential oil, whereas the presence of DS in excess produced an enriched essential oil with low toxicity. Furthermore, the antagonistic effect of DS and DDS against the other components of EO was shown by the application of two equations obtained from the literature. Their larvicidal performances were correlated, for the first time, with their detailed chemical composition. Data analysis strongly indicated the toxicity of the other EO sulfur ingredients.

Comparison of distillation and ultrasound-assisted extraction methods for the isolation of sensitive aroma compounds from garlic (Allium sativum).

A comparative study of traditional simultaneous distillation extraction (SDE), microwave assisted hydrodistillation extraction (MWHD) and ultrasound-assisted extraction (USE) is presented, for the extraction of essential oils from fresh garlic (Allium sativum) cloves. Each method is evaluated in terms of qualitative and quantitative composition of the isolated essential oil. The highly reactive sulfur molecules of the garlic volatile fraction show variable response to the different isolation methods. The application of ultrasound for the extraction of the essential oil is considered to cause a lesser damage of thermal-sensitive molecules, thus, providing a better approach of the compounds primarily responsible for the characteristic odor and taste of freshly chopped garlic. All heat-involving isolation procedures have been shown to differentiate the volatile-fraction profile as analyzed by GC-MS. Especially when grouping the compounds into cyclic and acyclic, the percentage concentrations drop from 77.4% to 8.7% for the acyclic while that of the cyclic compounds increase from 4.7% to 70.8%. The observed fact may be attributed to the effect of the heat applied, which changes from harsh thermal treatment (SDE) to short time thermal (MWHD) and room-temperature isolation (USE). The use of USE proves to be crucial in order to provide reliable insight into garlic's chemistry.