Bemisia tabaci (Gennadius) is an economically important pest of agricultural and ornamental plants worldwide and is now widely recognized as a cryptic species complex. In North America, B. tabaci is a particularly important pest of greenhouse poinsettia. In poinsettia production, two cryptic species from the B. tabaci complex, Mediterranean and Middle East Minor 1, often infest crops simultaneously. Differences in pesticide susceptibility between these two cryptic species have the potential to influence growers' management decisions, including the use of biological control or insecticides, and the choice of insecticide active ingredient. However, the demographic behavior of mixed-species infestations in commercial greenhouses has yet to be investigated. We conducted a survey of B. tabaci populations in commercial greenhouses in Ontario, Canada, and provide evidence that under biological control-based management, Middle East Minor 1 can displace Mediterranean, whereas under insecticide-based management Mediterranean populations will persist. Furthermore, we comment on implications of this behavior on the management of B. tabaci, and comment on methods used to identify B. tabaci cryptic species.