This research investigated seasonal climate changes within greenhouses and the impacts they have on efficacy of the predatory mites Amblyseius swirskii and Neoseiulus cucumeris. Controlled environment chamber, greenhouse small-cage, and commercial greenhouse trials were conducted to determine which biological control agent is more efficacious for control of the pest western flower thrips (WFT), (Frankliniella occidentalis) on ornamental crops. When observed under laboratory conditions, predation and oviposition were increased at higher temperatures. Photoperiod and light intensity also have an impact on predatory mites. Predation rates for both mite species were greater when subjected to short day light conditions (8 h light, 11 W/m2). Climates typical of summer (higher temperature and light intensity, long day length), were most favourable in terms of predation and oviposition for A. swirskii. Neoseiulus cucumeris laid more eggs under short day as opposed to long day settings. In summer and winter greenhouse small cage trials, the performance of N. cucumeris and A. swirskii significantly reduced WFT numbers on potted chrysanthemum plants. However, in summer, A. swirskii provided significantly better thrips control than N. cucumeris. The number of adult mites recovered from plants was similar for both mite treatments in winter, while A. swirskii were present in higher numbers throughout the summer trials. Results from leaf damage assessments indicate that A. swirskii is more effective for control of heavy WFT feeding damage in both summer and winter. Results from commercial greenhouse trials yielded similar trends as those found in the summer and winter small cage trials. / University of Guelph, Agriculture and Agri-Food Canada, Vineland Research and Innovation Center, Flowers Canada

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