-Known since ancient times, the phenomenon of allelopathy has recently received greater attention from researchers and farmers worldwide. Crop failures and low yields caused by the reseeding, overseeding, crop rotation and replanting of fruit trees in orchards are believed to be caused by allelopathic activity. Moreover, the expensive and environmentally impacting herbicides for weed control have motivated studies directed at developing cheaper, environmentally-friendly alternatives. Despite the difficulties in separating chemical interference from other mechanisms, more modern approaches have produced consistent and conclusive data on this topic. The release and dynamics of allelochemicals in the soil are discussed herein. Examples of allelopathic crops, the allelochemicals produced and their uses in cropping systems are also presented along with current research trends regarding allelopathy. allelopathy / chemical interference / agriculture / potential use

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RESUMOA espécie Sitophilus zeamais é uma das principais pragas do milho armazenado no Brasil. O controle é feito, comumente, utilizando-se medidas de higienização e limpeza, bem como inseticidas sintéticos fumigantes e protetores. A busca por produtos menos tóxicos, biodegradáveis e seguros do ponto de vista ecológico, é muito bem aceita pela sociedade. Assim, os objetivos do presente trabalho foram testar a toxicidade de contato e ingestão e fumigante de óleos essenciais e do composto orgânico natural eugenol para adultos de S. zeamais. Termos para indexação: Gorgulho do milho, bioatividade, plantas inseticidas, concentrações letais. ABSTRACTThe Sitophilus zeamais species is a major pest of stored maize in Brazil. The control is made, usually, using measures of hygiene and cleanliness, synthetic insecticides and fumigant protectors. The search for less toxic products, biodegradable and safe from an ecological point of view is very well accepted by society. The objective of this study was to test the toxicity by contact and ingestion and fumigant of essential oils and eugenol natural organic compound for adults of S. zeamais. The values of LC 50 in oil from leaves of Piper hispidinervum, Eugenia uniflora, Cinnamomum zeylanicum, P. marginatum, Schinus terebinthifolius, Melaleuca leucadendron, green fruits of S. terebinthifolius and eugenol compound in tests of contact and ingestion were estimated at 1.0; 11.6, 14.2, 21.1, 57.7, 75.8, 98.8 and 14.8 L/40 g maize, respectively. The toxicity ratios (TR) ranged from 1.3 to 98.8. In the fumigation of adults, the lethal concentrations ranged from 0.53 to 94.7 L/L air, in the following order of toxicity: P. hispidinervum > P. aduncum > S. terebinthifolius > green fruits of S. terebinthifolius > P. marginatum > eugenol, and the TR ranged from 2.0 to 178.7.

RESUMO:O óleo essencial obtido por hidrodestilação das folhas de Eugenia punicifolia, coletados a partir de duas regiões de Matas Serranas do Estado de Pernambuco (Serra Negra e Brejo da Madre de Deus), foi analisado por CG/EM. O monoterpeno oxigenado, linalol (SN: 44,0%, BMD: 61,2%), foi o componente principal do óleo de ambas amostras. Cerca de 66,2% da constituição dos voláteis da amostra proveniente de SN e 74,2% de BMD referem-se aos monoterpenos oxigenados, enquanto 33,6% da amostra de SN e 20,5% de BMD são sesquiterpenos oxigenados, sendo o β-cariofi leno o mais abundante (SN: 22,7%, BMD: 16,2%). Com exceção do α-cadinol, presente apenas no óleo proveniente do Brejo da Madre de Deus, a constituição química de ambas as amostras foi à mesma, variando apenas o percentual relativo de seus constituintes.Unitermos: Eugenia punicifolia, Myrtaceae, óleo essencial, linalol, β-cariofi leno, Matas Serranas.ABSTRACT: "Comparative study of the essential oil of Eugenia punicifolia (HBK) DC. from diferent places of Pernambuco". The essential oils obtained from the leaves of Eugenia punicifolia by hydrodistillation, which were collected from two different locations of Pernambuco (Serra Negra and Brejo da Madre de Deus), have been investigated by GC/MS. Linalol was found to be the main component of this oil from SN (44,0%) and BMD (61,2%). About 66,2% of the oil constituents from SN and 74,2% from BMD are oxygenated monoterpenes, with predominance of β-cariofi leno (SN: 22,7 and BMD: 16,2%). With exception of α-cadinol, present only in the oils from plants colleted in Brejo da Madre de Deus, the chemical composition of both samples was quite similar, the only difference was the relative content among their components.

Tetranychus urticae is considered one of the main plagues in the world. Its occurrence in Pernambuco was registered for the first time in 1985 and it has caused considerable damage to the farmers, attacking different cultures of agricultural interest. The essential oils from different parts of Vitex agnus-castus harvested in the Atlantic forest in the state of Pernambuco, Brazil, were obtained by hydrodistillation and the acaricidal potential was evaluated against Tetranychus urticae using two methods under laboratory conditions. Gas chromatography-mass spectrometry revealed the presence of 47 components accounting for 98.8 ± 0.0%, 93.0 ± 0.1% and 97.4 ± 1.0% of the essential oils from the leaves, fruit and inflorescence, respectively. The compounds 1,8-cineole and β-(E)-farnesene were the major components of the oils from the leaves (17.6 ± 0.3% and 13.6 ± 0.2%, respectively) and fruit (17.5 ± 0.1% and 15.4 ± 0.0%, respectively). β-(E)-farnesene (13.5 ± 0.1%) and β-caryophyllene (11.7 ± 0.1%) were the major components of the oils from the flowers. Acaricidal action varied depending on the part of the plant and method employed. Through fumigation, the oil from the leaves (CL 50 = 0.61 μL L -1 of air) was approximately six fold more toxic than the oil from the fruit. However, through residual contact, the oil from the fruit (CL 50 = 137.11 μLmL -1 ) was 1.1 fold more toxic than the oil from the leaves. The relationship between the chemical composition of the oils and acaricidal activity is also presented.