Abstract
Releases of Eretmocerus eremicus Rose and Zolnerowich (Hymenoptera: Aphelinidae) at release rates of 3.0-7.5 females per plant per week successfully suppressed whitefly populations on commercial poinsettia (Euphorbia pulcherrima Willd. ex Koltz.) crops in fall of 1996 at four Massachusetts commercial producers. At two sites, the whitefly populations consisted exclusively of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and at the other two sites exclusively of silverleaf whitefly, Bemisia argentifolii Bellows and Perring. Parasitoids were received from commercial suppliers and monitored weekly to determine the sex ratio of newly emerged adults, as well as the rate of adult emergence. Commercially produced pupae were 48.1% ( 2.2 SE) female and had 58.1% ( 3.6 SE) emergence under greenhouse conditions. Plants from the four biological control greenhouses in this trial at the time of sale of the crop had an average of 0.55 ( 0.28 SE) nymphs per leaf. Chemically-protected poinsettias offered for sale at eight local retail outlets had an average of 0.16 ( 0.09 SE) nymphs per leaf. Final whitefly densities in both biological control and insecticide-treated greenhouses were acceptable to consumers. An average of 6.8 insecticide applications was applied to suppress whiteflies in chemical control greenhouses in this trial, compared to 1.7 in the biological control greenhouses. Use of biological control was 27 fold more expensive, costing $2.14 per plant compared to $0.08 for chemical control. Cost of biological control was inflated by three factors: (1) an incorrectly high estimate by one grower of number of plants per greenhouse, (2) an unusually long production period (23 weeks) for one grower, and (3) miscommunication with the insectary concerning manner of filling orders to compensate for reduced percentage of emergence of adult parasitoids from ordered parasitized nymphs. Control of these cost-inflating factors would allow some reduction in the cost of the use of this parasitoid, but not to levels competitive with current pesticides. This study is the first to demonstrate the ability of E. eremicus releases to suppress T. vaporariorum populations in commercial poinsettia crops and parasitism of T. vaporariorum by E. eremicus was 7.5-fold higher (ave. 24.8% parasitism of fourth instar nymphs in pooled seasonal samples) than that observed in B. argentifolii (ave. 3.3%).
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