Assessment of cost and performance of Eretmocerus eremicus (Hymenoptera : Aphelinidae) for whitefly (Homoptera : Aleyrodidae) control in commercial poinsettia crops

Releases of Eretmocerus eremicus Rose and Zolnerawich (Hymenoptera: Aphelin idae) at release rates of 3.0-7.5 females per plant per week successfully s uppressed whitefly populations on commercial poinsettia (Euphorbia pulcherr ima Willd. ex Koltz.) crops in fall of 1996 at four Massachusetts commercia l producers. At two sites, the whitefly populations consisted exclusively o f greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and at the oth er two sites exclusively of silverleaf whitefly Bemisia argentifolii Bellow s and Perring. Parasitoids were received from commercial suppliers and moni tored 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 conditi ons. Plants from the four biological control greenhouses in this trial at t he 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 reta il outlets had an average of 0.16 (+/- 0.09 SE) nymphs per leaf. Final whit efly densities in both biological control and insecticide-treated greenhous es 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 biolo gical control was 27 fold more expensive, costing $2.14 per plant compared to $0.08 far chemical control. Cost of biological control was inflated by t hree factors: (1) an incorrectly high estimate by one grower of number of p lants per greenhouse, (2) an unusually long production period (23 weeks) fo r one grower, and (3) miscommunication with the insectary concerning manner of filling orders to compensate for reduced percentage of emergence of adu lt parasitoids from ordered parasitized nymphs. Control of these cost-infla ting factors would allow some reduction in the cost of the use of this para sitoid, but not to levels competitive with current pesticides. This study i s the first to demonstrate the ability off. 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%).