Whitefly infestation of poinsettias arises frequently from cuttings that were infested at the start of the season. Experiments were conducted to investigate the feasibility of using short-term elevated CO2 to eliminate whiteflies on cuttings prior to planting. Results indicated that adult greenhouse whiteflies (Trialeurodes vaporarium) are highly susceptible to an elevated level of CO2. All adult whiteflies are killed after exposure to 25% or 50% CO2 for less than 10 hours. Eggs, however, are more resistant than adults where 80% survived 10-hr of 50% CO2 treatment. Tests on poinsettia cuttings demonstrated that prolonged exposure to elevated CO2 resulted in the development of toxic symptoms soon after the treatments. Tolerance of 'Lilo' exceeded that of 'Supjibi', revealing differences in susceptibility of the two cultivars to the elevated CO2 treatment. Believing that the reduction in O2, rather than the elevation of CO2, was the main cause of mortality, we are currently testing the effects of hypoxia on survival of whiteflies.