Pyrethroid insecticides induce an excito-repellent effect that reduces contact between humans and mosquitoes. Insecticide use is expected to lower the risk of pathogen transmission, particularly when impregnated on long-lasting treated bednets. When applied at low doses, pyrethroids have a toxic effect, however the development of pyrethroid resistance in several mosquito species may jeopardize these beneficial effects. The need to find additional compounds, either to kill disease-carrying mosquitoes or to prevent mosquito contact with humans, therefore arises. In laboratory conditions, the effects (i.e., repellent, irritant and toxic) of 20 plant extracts, mainly essential oils, were assessed on adults of Anopheles gambiae, a primary vector of malaria. Their effects were compared to those of DEET and permethrin, used as positive controls. Most plant extracts had irritant, repellent and/or toxic effects on An. gambiae adults. The most promising extracts, i.e. those combining the three types of effects, were from Cymbopogon winterianus, Cinnamomum zeylanicum and Thymus vulgaris. The irritant, repellent and toxic effects occurred apparently independently of each other, and the behavioural response of adult An. gambiae was significantly influenced by the concentration of the plant extracts. Mechanisms underlying repellency might, therefore, differ from those underlying irritancy and toxicity. The utility of the efficient plant extracts for vector control as an alternative to pyrethroids may thus be envisaged.

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Essential oil samples of Cinnamosma fragrans from two regions in Madagascar, Tsaramandroso (38 samples) and Mariarano (30 samples), were analysed by GC/MS. Fifty-seven components were identified, accounting from 88.3% to 99.4% of the oils' composition. The major components were linalool (72.5 ± 23.3%) in Tsaramandroso and 1,8-cineole (47.3 ± 10.2%) in Mariarano. Samples B8 (95.8% linalool) from Tsaramandroso and B143 (71.6% 1,8-cineole) from Mariarano containing the highest proportions of the two main components identified, were selected to determine antimicrobial activities against 10 microbial strains. Bacillus subtilis and Staphylococcus aureus were the most sensitive strains to both oils. Minimum inhibitory concentration (MIC) values were lower for B143 against all tested Gram-negative strains than pure 1,8-cineole. B8 showed higher MIC values than pure linalool against Salmonella typhimurium and Vibrio alginolyticus, and similar MIC values to linalool towards the other Gram-negative strains. Both essential oils exhibited higher MIC values towards Fusarium oxysporum than their respective pure major component. These results suggested the occurrence of synergism or antagonism effects between the different oil constituents.

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The valorization of extracts from Brazilian vetiver (Vetiveria zizanioides (L.) Nash ex Small) roots was studied. This study took into account the extraction method, the chemical composition of the extracts, their sensorial characteristics, and the possibility of chemical transformations of the product. The performed extraction methods were hydrodistillation and extraction with supercritical carbon dioxide. Some pretreatment methods were tested on the vetiver roots and evaluated in terms of extraction yield, process time, chemical composition, and sensorial properties. Supercritical carbon dioxide extraction resulted in high yield (3.2%) in significantly less time than the other methods. The chemical compositions of the extracts obtained by the different methods were also compared to those of commercial vetiver oils from other sources, showing that Brazilian samples had a greater acid amount. An extraction in basic medium from Brazilian vetiver oil was done to remove its main acid (zizanoic acid), which was chemically transformed into an alcohol (khusimol) of desirable sensorial properties. Sensory evaluation indicated that the Brazilian volatile oil without acid could be used in perfumery and the extract obtained with supercritical carbon dioxide could have application in food.

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Recebido em 11/12/03; aceito em 15/6/04; publicado na web em 8/10/04 ESSENTIAL OILS FROM Myrcia SPECIES NATIVE TO RIO GRANDE DO SUL. Essential oils from M. richardiana, M. arborescens, M. selloi, M. oligantha, M. rostrata, M. lajeana, M. obtecta, M. pubipetala and M. hatschbachii were obtained by hydrodistillation and analyzed by GC and GC/MS. Sixty-seven compounds have been identified ranging from 90-99% of the oil contents. All analyzed species were rich in cyclic sesquiterpenes (66-99%), mainly those from the cadinane, caryophyllane and germacrane cyclization pathway, among them β-caryophyllene, germacrene D, bicyclogermacrene, δ-cadinene, spathulenol, caryophyllene oxide, globulol and α-cadinol. The acyclic sesquiterpene series was well represented by M. lajeana (32.1%), with 25,3% of (E)-nerolidyl acetate.Keywords: Myrcia; essential oil; Myrtaceae. INTRODUÇÃO Obtenção do óleo volátilO óleo volátil foi obtido a partir das folhas frescas, reduzidas com o auxílio de triturador mecânico e submetidas à hidrodestilação em processo contínuo com aparelho Clevenger, durante 5 h. O cál-culo de rendimento foi realizado através da relação do volume de óleo volátil recolhido do aparelho de Clevenger com a massa de material vegetal utilizada na extração 12 .

The essential oils obtained by steam distillation from the leaves of nine Eucalyptus species (E. cinerea F. Muell., E. baueriana F. Muell., E. smithii R. T. Baker, E. bridgesiana R. T. Baker, E. microtheca F. Muell., E. foecunda Schau., E. pulverulenta Sims, E. propinqua Deane and Maiden, E. erythrocorys F. Muell.) of Moroccan origin have been analysed using GC and GC–MS. A total of 83 constituents were identified. All the species investigated were found to possess an oil rich in 1,8‐cineole (>68%). In five species (E. cinerea F. Muell., E. baueriana F. Muell., E. smithii R. T. Baker, E. bridgesiana R. T. Baker and E. microtheca F. Muell.), the 1,8‐cineole content exceeded 80%. Copyright © 2004 John Wiley & Sons, Ltd.