A choice experiment was first conducted to measure the preference of adult whiteflies for cucumber versus poinsettia. This experiment is referred to as an unconditional choice test because the whiteflies had no prior experience with either host plant. Experimental arenas were created in BugDorm-3120 cages (60 x 60 cm: MegaView Science Education Services Co Taichung, Taiwan) or BugDorm-4180 cages(93 x 48 x 48 cm). The experiment was carried out at 20-25°C and a L14:D10 photoperiod in a research greenhouse. One potted cucumber(cv Marketmore 76: 4-5 weeks old from seed) and one potted poinsettia(cv Freedom Red': 8-10 weeks old from propagated cutting) were placed 25 cm apart from center to center in a cage.The location of the two plants in a cage was randomly assigned to the left or right side of the cage.One-hundred adult whiteflies (mixed age and sex) were collected from the whitefly colony in a 25 ml glass vial.The vial was capped with a plastic lid and placed between the two plants and whiteflies were released by opening the plastic lid. The number of adult whiteflies on the underside of the leaves was counted by carefully lifting and tilting the potted plant. The counting rarely induced whiteflies to fly off from the plant(personal observation)observations were made at 6,24,48 and 72 h after the release. The test was replicated 12 times with six replicates during each of two time periods.