Evaluation of Concentrated Releases of Parasitoids for the Control of Whiteflies on Poinsettia G. Amoroso, P. Frangi and R. Piatti Fondazione Minoprio Centro MiRT, Vertemate con Minoprio (CO) Italy Keywords: biological control, Bemisia tabaci, Encarsia formosa, Eretmocerus spp., Euphorbia pulcherrima, Trialeurodes vaporariorum Abstract Whiteflies are considered the most serious insect pest in greenhouse poinsettias. Research on alternative strategies to chemical control has successfully introduced the biocontrol with parasitoids. Shipping cost of parasitoids is the main constraint for the diffusion of biocontrol. This experiment was conducted to evaluate the effectiveness of concentrated releases of parasitoids for pest control on poinsettia grown in greenhouse, in order to induce an early biocontrol of the whiteflies Bemisia tabaci and Trialeurodes vaporariorum and reduce shipping costs. Two biological products were used: one with both Encarsia formosa and Eretmocerus spp. and the other with an E. formosa strain able to control both B. tabaci and T. vaporariorum. The parasitoid treatments were compared with a chemical control (thiamethoxam) and with a non-treated test. Results showed that during poinsettia cultivation whitefly control with 4 concentrated releases was not significantly different from the traditional 8 releases program. No differences in the effectiveness of the two biological products used were observed. A single drenching treatment with thiamethoxam 6 weeks after potting was very effective in controlling whiteflies. At the end of the trial the effectiveness of biological products was similar to the chemical treatment in adult whiteflies control. Nymph whiteflies biological control was slightly beyond the economic threshold of 2 live nymphs per leaf. INTRODUCTION Sweetpotato whitefly (Bemisia tabaci Gennadius) and greenhouse whitefly (Trialeurodes vaporariorum Westwood) (Homoptera: Aleyrodidae) continue to be the most important insect pests in commercial poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) all around the world. The control of whiteflies is frequently based on chemical treatments with systemic formulations (i.e. imidacloprid or thiamethoxam). These products are very effective against whiteflies, however resistance cases are now documented in literature (Bouharroud et al., 2003; Gorman et al., 2003; Prahbaker et al., 1997). It is necessary to decrease the dependence on a single control tactic. Biological control becomes a valid alternative way to control greenhouse pests. While biological control against whiteflies in greenhouse crops has been available since 1970s, the approach has not been adopted by growers because such programs are more expensive than the use of pesticides. However, progress has been made in lowering the cost and now this strategy is more frequently adopted (Van Driesche et al., 2002). Several types of beneficial organisms are available for biological control of whiteflies (Van Lenteren, 2000; Amoroso et al., 2005). Nowadays the parasitic wasps Encarsia formosa Gahan and Eretmocerus spp. (Hymenoptera: Aphelinidae) are commonly used in the management of whiteflies in greenhouse crops (Gerlin et al., 2001; Van Driesche and Lyon, 2003). Eretmocerus spp. can control sweetpotato whitefly, but not the glasshouse whitefly while Encarsia formosa is mainly effective against the greenhouse whitefly (Greer, 2000). Consequently, a combination of the two parasitic wasps is normally used to control whiteflies. The aim of this study was to evaluate the effectiveness of one E. formosa strain able to control both greenhouse and sweetpotato whitefly in order to reduce the cost of 1479 Proc. IS on Greensys2007 Eds.:S. De Pascale et al. Acta Hort. 801, ISHS 2008