Oviposition deterrent activity of basil plants and their essentials oils against Tuta absoluta (Lepidoptera: Gelechiidae).

The leafminer Tuta absoluta Meyrick (Lepidoptera: Gelechiidae) is one of the most important pests of tomato, reducing crop yields by up to 100% in greenhouses and fields, in several countries globally. Because synthetic insecticides lead to resistance and have adverse effects on natural enemies and the health of producers, alternative control methods are needed. In this study, we assessed the oviposition-deterring effect of basil plants, Ocimum gratissimum L. and O. basilicum L. (Lamiaceae), using dual-choice behavioural assays performed in flight tunnels. We found that both plants significantly reduced T. absoluta oviposition behaviour on a tomato plant located nearby. To evaluate the potential effect of basil volatile organic compounds, we formulated essential oils of both plant species in paraffin oil, and observed a similar oviposition-deterring effect. Gas chromatography analyses detected 18 constituents in these essential oils which the major constituents included thymol (33.3%), p-cymene (20.4%), γ-terpinene (16.9%), myrcene (3.9%) in O. gratissimum and estragol (73.8%), linalool (8.6%), ß-elemene (2.9%) and E-ß-ocimene (2.6%) in O. basilicum. Twenty and 33 compounds were identified of the volatiles collected on O. gratissimum and O. basilicum plants, respectively. The main components include the following: p-cymene (33.5%), γ-terpinene (23.6%), α-terpinene (7.2%), α-thujene (6.7%) and E-α-bergamotene (38.9%) in O. gratissimum, and methyl eugenol (26.1%), E-ß-ocimene (17.7%), and linalool (9.4%) in O. basilicum. Four compounds (α-pinene, ß-pinene, Myrcene, Limonene) were common in essential oils and plants. Our results suggest the valuable potential of basil and associated essential oils as a component of integrated management strategies against the tomato leafminer.

Fast gas chromatography characterisation of purified semiochemicals from essential oils of Matricaria chamomilla L. (Asteraceae) and Nepeta cataria L. (Lamiaceae).

The chemical composition of Matricaria chamomilla L. and Nepeta cataria L. essential oils was determined by GC-MS on an apolar stationary phase by comparison of the characteristic fragmentation patterns with those of the Wiley 275L database. The GC-MS chromatograms were compared with those obtained by fast GC equipped with a direct resistively heated column (Ultra Fast Module 5% phenyl, 5 mx 0.1 mm, 0.1 microm film thickness). Analytical conditions were optimised to reach a good peak resolution (split ratio=1:100), with analysis time lower than 5 min versus 35-45 min required by conventional GC-MS. The fast chromatographic method was completely validated for the analysis of mono- and sesquiterpene compounds. Essential oils were then fractionated by column chromatography packed with silica gel. Three main fractions with high degree of purity in E-beta-farnesene were isolated from the oil of M. chamomilla. One fraction enriched in (Z,E)-nepetalactone and one enriched in beta-caryophyllene were obtained from the oil of N. cataria. These semiochemical compounds could act as attractants of aphid's predators and parasitoids.