Chemical composition and acaricidal activity of the essential oils from Vitex agnus-castus L. (Verbenaceae) and selected monoterpenes

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 beta-(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). beta-(E)-farnesene (13.5 +/- 0.1%) and beta-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 (CL50 = 0.61 mu L 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 (CL50 = 137.11 mu LmL(-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.