Behaviour-modifying activity of eugenol on Thrips tabaci Lindeman

A series of observational bioassays were conducted to investigate the behavioural responses of the onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), to an application of a secondary plant compound to two different host plants with dissimilar leaf surface characteristics. Eugenol, a phenylpropanoid compound known to deter feeding and oviposition of the onion thrips, was applied to leek (Allium porrum L.) and cucumber (Cucumis sativus L.) at 1% concentration. Using a video system and special software for computing observational data, influences of this plant compound on the behaviour of T. tabaci females were evaluated. Eugenol treatment significantly prolonged the time periods thrips spent being inactive and moving across the treated leek or cucumber surface. The feeding periods on leek leaves treated with eugenol were clearly shorter compared to periods on untreated leek. The behaviours related to oviposition on leaves from both host species treated with eugenol were slightly reduced. T. tabaci females avoided direct contact with eugenol particularly when applied to leek, showing significantly lower contact duration compared to an untreated surface. This shows that behaviour-modifying secondary compounds such as eugenol may be used in various strategies and may contribute to the enhancement of current biological control measures and/or form novel components of Integrated Pest Management strategies.