Chemical constituents of essential oils of muña, Bolivian plants traditionally used as pesticides, and their insecticidal properties against Chagas' disease vectors

Chemical Composition of the Essential Oil From Minthostachys acris Schmidt-Leb. Grown in the Peruvian Andes

The chemical composition of the essential oil from aerial parts of Minthostachys acris Schmidt-Leb. grown in Cuzco was studied. A total of 59 volatile compounds were identified by gas-chromatography-flame ionization detector and gas chromatography-mass spectrometry in the essential oil obtained by steam distillation, of which the most prominent were pulegone (54.4%), cis-menthone (11.0%), and thymol (6.3%).

Chemical Composition and Antioxidant Activity of the Essential Oil from Hedeoma mandoniana Grown in Cuzco

The chemical composition of the essential oil from aerial parts of Hedeoma mandoniana Wedd. grown in Cuzco was studied. A total of 125 volatile compounds were identified in the essential oil, of which the most prominent were pulegone (35.3%), trans-menthone (9.8%) and limonene (9.2%). The essential oil had a low radical-scavenging activity determined by the ABTS method.

Insecticidal action of synthetic girgensohnine analogues and essential oils on Rhodnius prolixus (Hemiptera: Reduviidae)

Introducción. El alcaloide natural girgensohnina se ha usado como modelo en la síntesis de nuevos análogos de alcaloidales alfa-aminonitrílicos con efecto insecticida en vectores de enfermedades.Objetivo. Evaluar la actividad biocida de análogos de girgensohnina y de aceites esenciales de las plantas Cymbopogon flexuosus, Citrus sinensis y Eucalyptus citriodora en ninfas de estadios I y V de Rhodnius prolixus.Materiales y métodos. Se empleó la aplicación tópica en terguitos, esternitos y superficies tratadas con diferentes dosis exploratorias de cada una de las moléculas y aceites esenciales para determinar las dosis letales (LD50 y LD95).Resultados. El análogo 3 tuvo la mayor actividad insecticida, con una mortalidad de 83,3±16,7% en los terguitos, de 38,9±4,8 % en los esternitos y de 16,7±0 % a las 72 horas en ninfas de estadio I expuestas a superficies tratadas y 500 mg.L-1. En las ninfas de estadio V solo se presentó mortalidad en los esternitos (11,1±9,6 % con el análogo 6 y 5,5±4,7 % con los análogos 3 y 7 a las 72 h y 1.500 mg.L-1). Las dosis letales para la molécula 3 en los terguitos de ninfas de estadio I fueron las siguientes: DL50, 225,60 mg.L-1y DL95, 955,90 mg.L-1. En cuanto a los aceites esenciales, el efecto insecticida solo se presentó con C. flexuosus (11,1±4,8%) en los esternitos de ninfas de estadio I expuestas a superficies tratadas; con C. sinensis (5,6±4,8%) en los terguitos y en los esternitos (8,3±0%) a las 72 horas y 1.000 mg.L-1.Conclusión. Los análogos sintéticos del alcaloide girgensohnina y los aceites esenciales de C. flexuosus y C. sinensis exhibieron actividad insecticida en R. prolixus. El análogo 3 exhibió la mayor actividad insecticida de todas las moléculas evaluadas bajo las condiciones de laboratorio.

Repellency of the Components of the Essential Oil, Citronella, to Triatoma rubida, Triatoma protracta, and Triatoma recurva (Hemiptera: Reduviidae: Triatominae)

The kissing bugs--Triatoma rubida (Uhler), Triatoma protracta (Uhler), and Triatoma recurva (Stal)--are common hematophagous bugs in southeastern Arizona and responsible for severe allergic reactions in some individuals who are bitten. They also possess the potential to transmit the blood parasite, Trypanosoma cruzi. We previously found the essential oil, citronella, to be an excellent deterrent of feeding of T. rubida on a restrained mouse. In this work, we tested major components--alcohols, aldehydes, and monoterpenes--of citronella oil for repellency against the three common triatome species endemic in southern Arizona. The following citronella oil components--geraniol, citronellol, limonene, and citronellal--in different concentrations and combinations were tested. All components of citronella oil demonstrated some inhibition of feeding, ranging from very weak inhibition (limonene) to significant inhibition (geraniol and citronellol). A mixture of geraniol and citronellol was found to be repellant at concentrations of .165 and .165 vol%, respectively, for all three triatome species. Citronellal and limonene had no significant repellent activity. The repellent activity of citronella oil appears to be acting through direct contact with the bugs rather than diffusion of vapors.

Zanthoxylum caribaeum (Rutaceae) essential oil: chemical investigation and biological effects on Rhodnius prolixus nymph

A chemical investigation and bioassays against fifth-instar nymphae of the hematophagous insect Rhodnius prolixus, vector of Chagas disease, were conducted with the essential oil from Zanthoxylum caribaeum. The main results may be summarized as follows: (i) 54 components were identified, corresponding to 90.4% of the relative composition; sesquiterpenes (47.3%) and monoterpenes (41.2%) are the major constituents; (ii) muurola-4,5-trans-diene and isodaucene are described for the first time as chemical constituents of the essential oil from leaves of this species; (iii) topical treatment with the crude essential oil induced high levels of paralysis (from 18.88 to 33.33%) and mortality (from 80 to 98.9%) depending on the dose applied (0.5 to 5.0 μl per insect); (iv) feeding treatment with the crude essential oil also induced high levels of mortality (from 48.8 to 100%) but low levels of paralysis (from 2.22 to 7.77%) depending on the dose applied (0.5 to 5.0 μl/ml of blood); (v) in the continuous treatment, only the dose of 5.0 μl/cm(2) was able to promote statistical significant levels of mortality (63.3%) but no paralysis were detected. However in this group, occasionally, only few insects displayed malformations of legs and wings after treatment; and (vi) any treatment was able to disrupt the metamorphosis process since the low adult stage emergence observed to all groups was due the high insect mortality. These observations suggest the interference of Z. caribaeum compounds on the triatomine neuroendocrine system. The significance of these results in relation to the relevant biological events in R. prolixus as well as the possible use of insect growth regulators present in Z. caribaeum oil in integrated vector control programs against hematophagous triatomine species is herein discussed.

Behavioral and toxicological responses of Rhodnius prolixus and Triatoma infestans (Hemiptera: Reduviidae) to 10 monoterpene alcohols

The effect on locomotor activity, the repellency, and the knock-down produced by 10 monoterpene alcohols were evaluated on first-instar nymphs of Rhodnius prolixus and Triatoma infestans, vectors of Chagas disease. A video tracking technique was used to evaluate locomotor activity and repellency by exposure to papers impregnated with monoterpenes. Eugenol on R. prolixus and (S)-cis-verbenol on T. infestans did not modify the locomotor activity. The remaining monoterpenes produced hyperactivity on both species, although the concentration required was at least a 1,000 times higher than that of deltamethrin (positive control). Carvacrol, eugenol, and geraniol resulted as repellent as N,N-diethyl-m-toluamide (positive control) for both species. A similar result was observed for almost every monoterpene on T. infestans. Knock-down effect was evaluated by exposing the nymphs in closed recipients. The order of increasing toxicity on R. prolixus was (KT50 values in min): geraniol (213.7) < alpha-terpineol (164.5) < linalool (124.2) < carvacrol (111.6) < eugenol (89.8) < thymol (78.9), and on T. infestans: alpha-terpineol (289.8) < eugenol (221.3) < carvacrol (164.2) < linalool (154.9) < thymol (96.7). All monoterpenes were less toxic than the positive control, dichlorvos (3.6 min for R. prolixus and 3.9 min for T. infestans). After 7 h of exposure, (-)-carveol, citronellol, and menthol (on both species) and geraniol (on T. infestans) produced < 50% of knock-down. After these results, it is worthwhile to explore more deeply the potential of these compounds as tools for controlling Chagas disease vectors.

Repellency of DEET, picaridin, and three essential oils to Triatoma rubida (Hemiptera: Reduviidae: Triatominae)

The kissing bug, Triatoma rubida (Uhler) is a common hematophagous bug in Tucson, AZ, and is responsible for causing severe allergic reactions in some bitten individuals. DEET, picaridin, tea tree oil, peppermint oil, and citronella oil were tested for repellency to T. rubida and its ability to probe and feed on a small restrained rat. No long range repellency was observed with any of the test materials. The lowest repellent concentrations observed were: 10% DEET, 7% picaridin; 30% tea tree oil, 3.3% peppermint oil, and 0.165% citronella oil. Only citronella oil was able to stop all probing and feeding by T. rubida. Citronella oil appears to be a promising potential repellent to prevent sleeping people from being bitten by kissing bugs.

Volatile organic compounds from rhizobacteria increase biosynthesis of essential oils and growth parameters in peppermint (Mentha piperita)

Volatile organic compounds (VOCs), characterized by low molecular weight and high vapor pressure, are produced by all organisms as part of normal metabolism, and play important roles in communication within and between organisms. We examined the effects of VOCs released by three species of plant growth-promoting rhizobacteria (Pseudomonas fluorescens, Bacillus subtilis, Azospirillum brasilense) on growth parameters and composition of essential oils (EO) in the aromatic plant Mentha piperita (peppermint). The bacteria and plants were grown on the same Petri dish, but were separated by a physical barrier such that the plants were exposed only to VOCs but not to solutes from the bacteria. Growth parameters of plants exposed to VOCs of P. fluorescens or B. subtilis were significantly higher than those of controls or A. brasilense-treated plants. Production of EOs (monoterpenes) was increased 2-fold in P. fluorescens-treated plants. Two major EOs, (+)pulegone and (-)menthone, showed increased biosynthesis in P. fluorescens-treated plants. Menthol in A. brasilense-treated plants was the only major EO that showed a significant decrease. These findings suggest that VOCs of rhizobacteria, besides inducing biosynthesis of secondary metabolites, affect pathway flux or specific steps of monoterpene metabolism. Bacterial VOCs are a rich source for new natural compounds that may increase crop productivity and EO yield of this economically important plant species.

Toxicity of Schizonpeta multifida essential oil and its constituent compounds towards two grain storage insects

BACKGROUND

The essential oil derived from the flowering aerial parts of Schizonpeta multifida was investigated for insecticidal activity against two grain storage insects, maize weevil (Sitophilus zeamais) and red flour beetle (Tribolium castaneum).

RESULTS

The main constituents of the essential oil were menthone (40.34%) and pulegone (26.87%), followed by D-limonene (5.81%) and isomenthone (5.14%). Bioactivity-directed chromatographic separation on repeated silica gel columns led to the isolation of menthone and pulegone. Pulegone showed pronounced contact toxicity against S. zeamais and T. castaneum adults (7 day LD(50)= 4.46 and 1.55 µg per adult respectively) and was more toxic than menthone (7 day LD(50)=33.47 and 2.67 µg per adult respectively), while the crude essential oil had 7 day LD(50) values of 30.17 and 2.75 µg per adult respectively. Pulegone also displayed strong fumigant toxicity against S. zeamais and T. castaneum adults (7 day LC(50)=3.47 and 11.56 mg cm(-3) respectively) and was again more toxic than menthone (7 day L(50) =10.32 and 31.25 mg cm(-3) respectively), while the crude essential oil had 7 day LC(50) values of 8.33 and 26.41 mg cm(-3) respectively.

CONCLUSION

The essential oil of S. multifida and its two main components may have potential to be developed as new natural fumigants/insecticides for the control of stored product insects.

Fumigant insecticidal activity and repellent effect of five essential oils and seven monoterpenes on first-instar nymphs of Rhodnius prolixus

The aim of this study was to evaluate the fumigant and repellent activity of five essential oils (from eucalyptus, geranium, lavender, mint, and orange oil) and seven monoterpenes (eucalyptol, geraniol, limonene, linalool, menthone, linalyl acetate, and menthyl acetate) on first-instar nymphs of the bloodsucking bug Rhodnius prolixus Stahl (vector of Chagas disease in several Latin American countries). Fumigant activity was evaluated by exposing the nymphs to the vapors emitted by 100 microl of essential oil or monoterpene in a closed recipient. The knockdown time 50% (KT50) for eucalyptus essential oil was 215.6 min (seven times less toxic than dichlorvos, a volatile organophosphorus insecticide used as a positive control). The remaining essential oils showed a poor fumigant activity: < 50% of nymphs were knocked down after 540 min of exposure. The KT50 values for monoterpenes, expressed in minutes, were as follows: 117.2 (eucalyptol), 408.7 (linalool), 474.0 (menthone), and 484.2 (limonene). Eucalyptol was 3.5 times less toxic than dichlorvos. No affected nymphs were observed after 540 min of exposure to geraniol, linalyl acetate, or menthyl acetate. Repellency was quantified using a video tracking system. Two concentrations of essential oils or monoterpenes were studied (40 and 400 microg/cm2). Only mint and lavender essential oils produced a light repellent effect at 400 microg/cm2. Geraniol and menthyl acetate produced a repellent effect at both tested concentrations and menthone only elicited an effect at 400 microg/cm2. In all cases, the repellent effect was lesser than that produced by the broad-spectrum insect repellent N,N-diethyl-3-methylbenzamide (DEET).

Ethnobotany, biochemistry and pharmacology of Minthostachys (Lamiaceae)

AIMS OF THE STUDY

The South American mint genus Minthostachys is of great importance in the Andes as a medicinal, aromatic, culinary and commercial essential oil plant. After decades of taxonomic confusion and virtual indeterminability of specimens, new systematic and taxonomic work has been conducted in recent years. The present paper attempts to summarize the state of knowledge about Minthostachys with a focus on ethnobotany, analyses of essential oil content and pharmacology, to identify the currently accepted species names for the plants examined in these previous studies, and to assess where additional research is needed.

MATERIALS AND METHODS

All available studies on Minthostachys were obtained and evaluated. Herbaria were contacted to identify voucher specimens cited in the respective publications.

RESULTS AND CONCLUSIONS

The great majority of published studies was conducted on a single species, Argentinean Minthostachys verticillata. In contrast, the most widely distributed and well-known species (Minthostachys mollis) as well as several locally important and intensively used species (e.g., Minthostachys acutifolia) have received disproportionately little attention, and virtually nothing is known about the local endemics among the 17 species currently recognized. In many cases, however, it is difficult to relate the results to taxonomic entities due to the lack of voucher specimens. Future research efforts should especially be directed at studying the chemistry and potential for use of several common but so far neglected species of the central and northern Andes, at disentangling environmental and genetic influences on essential oil composition, at prerequisites for cultivation, and at the pharmacological basis of the most important traditional uses. Because of the morphological complexity of the genus, future researchers are urged to deposit voucher specimens of the plants used in their studies to facilitate species identification and to make the results more comparable and reproducible.

Insecticidal activity of menthol derivatives against mosquitoes

BACKGROUND

The insecticidal activity of essential oil of Mentha piperita L. emend. Huds. against local mosquitoes as disease vectors was recognized and found to be due to the presence of menthol, which is the major aroma compound of the oil. The minor compounds of the oil, i.e. menthone, beta-caryophyllene, menthyl acetate, limonene, alpha-pinene and pulegone, showed either less or no activity against the mosquitoes tested. L-Menthol derivatives were synthesized and their knockdown effect and mortality were evaluated against local mosquitoes of Culex quinquefasciatus Say, Aedes aegypti L. and Anopheles tessellatus Theobald as disease vectors. This is the first report of mosquitocidal activity of menthol and its derivatives against Cx. quinquefasciatus, Ae. aegypti and An. tessellatus.

RESULTS

Derivative synthesis followed by structure-activity relationship studies identified several derivatives, i.e. menthyl chloroacetate, menthyl dichloroacetate, menthyl cinnamate, menthone glyceryl acetal, thymol, alpha-terpineol and mugetanol, with enhanced mosquitocidal activity against Cx. quinquefasciatus, Ae. aegypti and An. tessellatus relative to the parent compound L-menthone.

CONCLUSION

In ester derivatives of L-menthol the optimum activity is dependent on the size and shape of the ester group and the presence of chlorine atoms in the ester group. In structurally related derivatives of L-menthol the optimum activity is dependent on the aromaticity, the degree of unsaturation, the position of the hydroxy group and the type of functional group.

Effects of mechanical wounding on essential oil composition and emission of volatiles from Minthostachys mollis

Plant tissues may show chemical changes following damage. This possibility was analyzed for Minthostachys mollis, a Lamiaceae native to Central Argentina with medicinal and aromatic uses in the region. Effects of mechanical damage on its two dominant monoterpenes, pulegone and menthone, were analyzed by perforating M. mollis leaves and then assessing essential oil composition at 24, 48, and 120 hr; emission of volatiles was also measured 24 and 48 hr after wounding. Mechanical damage resulted in an increase of pulegone and menthone concentration in M. mollis essential oil during the first 24 hr. These changes did not occur in the adjacent undamaged leaves, suggesting a lack of systemic response. Postwounding changes in the volatiles released from M. mollis damaged leaves were also detected, most noticeably showing an increase in the emission of pulegone. Inducible chemical changes in aromatic plants might be common and widespread, affecting the specific compounds on which commercial exploitation is based.

Quantitative variations in the essential oil of Minthostachys mollis (Kunth.) Griseb. in response to insects with different feeding habits

Plants display a diverse array of inducible changes in secondary metabolites following insect herbivory. Herbivores differ in their feeding behavior, physiology, and mode of attachment to the leaf surface, and such variations might be reflected in the induced responses of damaged plants. Induced changes were analyzed for Minthostachys mollis, a Lamiaceae with medicinal and aromatic uses, and four species of folivore insects with different feeding habits (chewing, scraping, sap-sucking, and puncturing). In M. mollis leaves experimentally exposed to the insects, levels of the two dominant monoterpenes pulegone and menthone were assessed 24 and 48 h after wounding. Menthone content generally decreased in the essential oil of damaged leaves, whereas pulegone concentration increased in all treatments. These changes occurred also in the adjacent undamaged leaves, suggesting a systemic response. The relatively uniform response to different kinds of damage could be attributable to the presence of such a strongly active compound as pulegone in the essential oil of M. mollis. The effects of wounding on essential oil concentration may be significant from a commercial point of view.