Pest Management Science Pest Manag Sci 63:910–917 (2007) Effectiveness of insecticide-treated and non-treated trap plants for the management of Frankliniella occidentalis (Thysanoptera: Thripidae) in greenhouse ornamentals Rosemarije Buitenhuis, 1∗ J Les Shipp, 1 Sarah Jandricic, 2 Graeme Murphy 3 and Mike Short 2 1 Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, Harrow, ON, Canada 2 Eco Habitat Agri Services, Grimsby, ON, Canada 3 Ontario Ministry of Agriculture and Rural Affairs, Vineland, ON, Canada Abstract: The effectiveness of trap cropping as an integrated control strategy against western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), was explored in potted chrysanthemum, Dendranthema grandiflora (Tzvelev), greenhouse crops. The efficacy of flowering chrysanthemum trap plants, either treated with the insecticide spinosad or untreated, to regulate F. occidentalis populations was tested at different spatial scales (small cage, large cage and commercial greenhouse) and for different time periods (1 or 4 weeks). It was demonstrated that flowering chrysanthemums as trap plants lower the number of adult F. occidentalis in a vegetative chrysanthemum crop and, as a result, reduce crop damage. In the 4 week large-cage trial and the commercial trial, significant differences between the control and the trap plant treatments started to appear in the third week of the experiment. Larvae were only significantly reduced by the presence of trap plants in the 1 week small-cage trials. There were no significant differences between treatments with spinosad-treated and untreated trap plants in the number of F. occidentalis on the crop. This suggests that there was minimal movement of adult F. occidentalis back and forth between the trap plants and the crop to feed and oviposit. It is concluded that the trap plant strategy is a useful tool for integrated pest management against F. occidentalis in greenhouses. Copyright  2007 Crown in the right of Canada. Published by John Wiley & Sons, Ltd Keywords: trap plants; Frankliniella occidentalis; integrated pest management; potted chrysanthemum; spinosad 1 INTRODUCTION Western flower thrips, Frankliniella occidentalis (Per- gande) (Thysanoptera: Thripidae), is a major pest of floricultural greenhouse crops. It causes direct feed- ing damage to flowers and foliage and can vector important plant pathogens such as tospoviruses. 1,2 In high-value crops, like potted ornamentals, there is a zero tolerance for any damage affecting the visual appearance of the crop, and in many instances the threshold is very low for F. occidentalis. 3,4 However, this pest is notoriously difficult to control. Its cryptic behavior, short development time, high reproductive ability and the potential for rapid development of resistance to many insecticides make it difficult to control chemically. 5–7 In addition, at present there are few selective pesticides for thrips control that may be integrated into existing biological control programs. 2 Finally, in many cases natural enemies do not suc- ceed or are not cost effective as the sole control measure in reducing F. occidentalis populations to a sufficiently low level to prevent damage to greenhouse ornamentals. 8 An effective pest management strategy against F. occidentalis probably should combine a range of control measures (chemical, biological, cultural and physical control options). The use of trap plants (i.e. plants that are deployed to attract and retain pest insects in order to reduce damage to the crop) is a cultural control method that can be integrated into an IPM program for F. occidentalis control. The major advantage of the trap plant strategy is that the pest is attracted and concentrated on the trap plants, and not on the crop. This situation permits the grower to use natural enemies (predators) or microbial control agents (entomopathogenic fungi or nematodes) for control of any residual pest populations on the crop. Until now, trap plants are mainly used in field crops 9–11 and gardening. Recent studies have shown that flowering chrysanthemums, Dendranthema grandiflora (Tzvelev), can be used as trap plants ∗ Correspondence to: Rosemarije Buitenhuis, Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, Harrow, ON, Canada E-mail: buitenhuisr@agr.gc.ca (Received 6 November 2006; revised version received 24 January 2007; accepted 25 March 2007) Published online 20 July 2007; DOI: 10.1002/ps.1426 Copyright  2007 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. Pest Manag Sci 1526–498X/2007/$30.00