Interest of semiochemicals against Frankliniella occidentalis in ornamental crops

Abstract: The western flower thrips (WFT) Frankliniella occidentalis is the main pest of
greenhouse crops in horticultural production. IPM strategies use mainly phytoseiid massreleases to control the larval stage of the pest. However, the adult stage, with a much longer life, is not targeted by this approach. Its control requires combined methods, part of which may be the exploitation of semiochemical compounds. This study was initiated to determine WFT responses to plant odour compounds, essential cues in thrips host finding. Laboratory, cages and greenhouse tests investigated the biological properties of thyme (Thymus zygis), wintergreen (Gaultheria fragrantissima) and oregano (Origanum compactum) essential oils at 1 % and 0.1 % and thymol. These experiments highlighted the repellent properties of T. zygis and G. fragrantissima (61.5 % and 60.7 %, respectively). In cage, pure application of essential oil of thyme by passive diffusion induces a 75 % decrease of oviposition activity. Active application by cold nebulization essential oil improved this efficiency (-89 % larvae on leaves). Greenhouses trials confirmed their repellent properties in decreasing adult trapping on odourbaited-trap (81 % with thyme and 33 % with wintergreen). On a larger scale, the oviposition deterrent has not been demonstrated. Only a change in the distribution of damage has been observed when thyme was nebulized in verbena crop. Although thymol is the most promising compound for use as a repellent against WFT, its registration for use by growers is complex. A new project proposes to work on a push-pull approach using newly formulated compounds in verbena and pepper crops.