Biological control of western flower thrips, F rankliniella occidentalis ( P ergande) ( T hysanoptera: T hripidae), in gerberas, chrysanthemums and roses

F rankliniella occidentalis ( P ergande), western flower thrips ( WFT ), is a major worldwide pest of vegetables and ornamental crops. The biology of WFT was examined on gerberas, chrysanthemums and roses in relation to plant stage (flowering and non‐flowering), pupation site, soil moisture and plant parts often inhabited by adult and immature thrips. Four foliage thrips predators ( T ranseius montdorensis ( S chicha), O rius armatus ( G ross), M allada signata ( S chneider) and N eoseiulus cucumeris ( O udemans)) and three soil predators ( G eolaelaps aculeifer ( C anestrini), S teinernema feltiae ( F ilipjev) and D alotia coriaria ( K raatz)) were studied to determine their ability to reduce the numbers of WFT on gerberas, chrysanthemums and roses. There was no difference in the number of adults that emerged from growing media of high or low moisture content on any host plant. There were also no differences in the total numbers of WFT recaptured from flowering gerberas, chrysanthemums or roses. However, about seven times the number of thrips were collected from flowering chrysanthemums compared with non‐flowering chrysanthemums, indicating that the flowering plants were more suitable hosts. Of all thrips recollected, the greatest percentage was immature (larval and pupal) thrips (70%, 71% and 43%) on the flowers for gerberas, chrysanthemums and roses, respectively. The mean percentage of thrips that emerged as adults from the soil was very low (5.3 ± 1.2, 8.5 ± 2.9, 20.5 ± 9.1 and 28.2 ± 5.6%) on gerberas, flowering and non‐flowering chrysanthemums, and roses, respectively. Simultaneous release of foliage and soil predators did not reduce the number of thrips beyond that caused by foliage predators alone. Of the foliage predators, T . montdorensis , O . armatus and N . cucumeris performed best, significantly reducing the numbers of adult and immature thrips on flowers and foliage by 30–99%. Further research is required to determine the most cost‐effective rates of release in cut flower crops.