Seasonal climatic variations influence the efficacy of predatory mites used for control of western flower thrips in greenhouse ornamental crops.

The influence of seasonal greenhouse climate on the efficacy of predatory mites for thrips control was determined for potted chrysanthemum. Trials in controlled environment chambers, small-scale greenhouses and commercial greenhouses were conducted to determine which biological control agent-that is, Amblyseius swirskii Athias-Henriot or Neoseiulus cucumeris (Oudemans)-is more efficacious for control of western flower thrips, Frankliniella occidentalis (Pergande), in different seasons. Under simulated summer conditions, no differences were observed in the predation and oviposition rates of both predatory mites in the laboratory trials. However, small-scale greenhouse trials showed that A. swirskii performed better than N. cucumeris in summer (i.e., more efficacious thrips control, higher predator abundance and less overall damage to the crop). Under simulated winter conditions, laboratory trials demonstrated variable differences in predation rates of the two predatory mites. The small-scale greenhouse trials in winter showed no differences in thrips control and predatory mite abundance between the two predatory mites, but plants with A. swirskii had less damage overall. The results from the small-scale trials were validated and confirmed in commercial greenhouse trials. Overall, A. swirskii performed better in the summer and equally good or better (less damage overall) under winter conditions, whereas N. cucumeris is a more cost effective biological control agent for winter months.