Mentha cervina L.: insectos e fungos associados. Propriedades insecticidas do óleo essêncial

Mestrado em Engenharia Agronómica - Instituto Superior de AgronomiaMentha L. is a genus of aromatic perennial herbs belonging to the family Lamiaceae distributed mostly in temperate and sub-temperate regions of the world. Different species of mint are used for their medicinal and aromatic properties, and cultivated for their essential oils and monoterpenes components of the oil, for use in food, flavour, cosmetic and pharmaceutical industries. Pests and pathogens of Mentha may cause substantial damage to the crop and considerable loss in oil yield. The concern about the negative effects caused by synthetic pesticides such environmental pollution, development of phenomena of resistance at treated insect populations and toxicity at different trophic levels led to a search for natural and environmentally friendly products. Plant extracts can be an alternative for a pest management with little harmfulness to environment. The present study was aimed at the repellent/insecticidal properties of Mentha cervina L. essential oil (EO) against ants, the identification of the insects associated to M. cervina and M. pulegium L., and fungi associated to M. cervina. The essential oils were obtained by hidrodestillation by using Clevenger apparatus of dried plant material. Two species of ants - Tapinoma nigerrimum Nylander and Aphaenogaster senilis Mayr - were used to study the repellent/insecticidal properties of M. cervina oil. The experimental unit corresponded to a system of two compartments separated by a PVC pipe containing a layer of filter paper dampened with EO solutions. Groups of 10 insects per replicate were placed in one of the compartments. The opposite compartment contained food. This allowed the insects to come into contact with the treated papers. Four concentrations were tested and each was replicated three times for T. nigerrimum and five times for A. senilis. EO was dissolved in ethanol and prepared with distilled water with different concentrations: 2,5; 5;0, 10,0 and 20,0 μg/cm2. Distilled water and 1% (v/v) ethanol (96%) were used as control. The effects on T. nigerrimum mortality were evaluated after 24 to 144 hours. Concentration OE 2,5 μg/cm2 provided 70% mortality after 72 hours. The effects on A. senilis were evaluated after 24 to 196 hours. Concentration OE 2,5 μg/cm2 provided 72% mortality after 192 hours. Percent mortality data were analysed by ANOVA (SPSS v. 15.0), Tukey’s test was used to compare the difference between treatments. The plant materials studied were collected from seedbeds located at the Botanic Park of Tapada da Ajuda at the Agronomic Institut of the Technical University of Lisbon. In order to deepen knowledge about insects associated to M. cervina and M. pulegium, samples were surveyed from 39 accessions of M. cervina and 3 accessions of M. pulegium, in July, September, October and November 2008, weekly. The specimens collected were preserved in 70% ethanol for identification. In all, 604 insects were identified comprising 4 different orders and 15 families. The higher number of insects found belongs to the orders Coleoptera and Hemiptera. Mites were identified in 12 accessions of M. cervina, comprising 4 families and four species. In order to study the fungi associated to M. cervina, 30 accessions were selected. Samples were surveyed between October and November 2007, by visual observation of dried and/or necrotic plants. The surface sterilized roots and stems segments were evenly spaced in Petri dishes containingpotato dextrose agar (PDA) and potassium thiocyanate (KCNS 5%) medium. With the identification of the isolates, 12 genera were identified. The most predominant genera were Alternaria e Fusarium. These two genera and the species Colletotrichum coccodes and Sclerotinia sclerotiorum are cited in the literature as pathogenic to Mentha species.--------------------------------------Os objectivos do presente trabalho consistiram em determinar as propriedades repelentes/insecticidas do óleo essencial (OE) de Mentha cervina L. em formigas e em identificar, em cultura, os insectos e os fungos associados a M. cervina. Procedeu-se ainda ao levantamento de insectos associados a algumas populações M. pulegium L., também em cultura. Nos estudos sobre as propriedades repelentes/insecticidas em formigas das espécies Tapinoma nigerrimum Nylander e Aphaenogaster senilis Mayr utilizaram-se as seguintes concentrações de OE: 2,5, 5,0, 10,0 e 20,0 μg/cm2. Verificou-se algum efeito de repelência nas concentrações intermédias, os valores de mortalidade mais elevados ocorreram na concentração mais baixa. As amostragens dos insectos associados a M. cervina e foram realizadas nos meses de Julho, Setembro, Outubro e Novembro de 2008, semanalmente. A maioria dos insectos identificados pertence às ordens Coleoptera e Hemiptera. Ácaros também foram identificados em M. cervina, pertencentes a quatro famílias e quatro espécies. O levantamento dos fungos associados a M. cervina foi efectuado durante os meses de Outubro e Novembro de 2007. Nos géneros de fungos identificados predominaram Alternaria e Fusarium. Estes dois géneros e as espécies Colletotrichum coccodes e Sclerotinia sclerotiorum estão referenciadas como doenças de Mentha spp.