| Sumario: | The whitefly Bemisia tabaci Gennadius is the key pest of protected tomato production in Spain. The predominant form is biotype "Q", an efficient vector of tomato yellow leafcurl virus (TYLCV), which is the principal cause of damage. Although management has relied primarily on chemical control, factors such as overlapping crop cycles, insecticide resistance and public pressure have spurred development of alternative management tactics. These include TYLCV-tolerant varieties and pest exclusion methods that, along with more selective insecticides, have created a more compatible environment for biological control. Here we describe trials of an integrated pest management (IPM) system conducted during the fall season in 12 commercial greenhouses throughout the production area compared with 7 greenhouses utilizing only chemical control (termed "conventional"). Each IPM greenhouse was divided into 4 equal sections, two receiving weekly releases of the indigenous Eretmocerus mundus Mercet and two receiving the exotic Eretmocerus eremicus Rose & Zolnerowich. Fewer and more selective pesticides were used in IPM greenhouses compared to conventional greenhouses. Early use of broad-spectrum insecticides in IPM greenhouses appeared to be counterproductive in that establishment of parasitioids was delayed with no real gain in control. Incidence of parasitized whiteflies in IPM greenhouses averaged around 50%, with E. mundus predominating, compared to less than 3% in conve
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