Abstract: White flies Aleyrodes proletella (Hemiptera: Aleyrodidae) are serious insect pestsof vegetable brassica crops. Harvested products showing damage from white flies fail to meetquality standards, and are thus unmarketable. In spite of the availability of effectiveinsecticides, growers struggle to contain white flies in overwintering vegetable brassica cropssuch as kale (Brassica oleracea convar. acephala var. sabellica L.). As the cultivation of kaleincreases, so does the demand for management solutions, also because kale provides anoverwintering habitat to white flies and hence a reservoir endangering newly planted crops inthe following season. We investigated the effectiveness of late insecticide treatments in kaleand colonization success of overwintered white flies in comparison to white flies withoutoverwintering stimulus. We evaluated the efficacy of late-season insecticide treatments in thefield in two vegetable brassica crops with different plant architecture, savoy cabbage(Brassica oleracea convar. capitata var. sabauda L.) and kale. The tested products differed intheir effectiveness in protecting the two crops, in terms of the recovered number of eggs andlarvae of white flies.To study colonization of vegetable brassica crops early in the growing season, weperformed a greenhouse experiment and took morphological measurements. Field-collectedwhite flies reared through the winter on kale under greenhouse conditions (withoutoverwintering stimulus) and white flies exposed to typical winter weather conditions in thefield (with overwintering stimulus) were compared with respect to their ability to colonizenewly planted kale plants. Additionally, we measured the white flies’ forewing and abdomensize. White flies with and without overwintering stimulus differed in their colonizationsuccess measured in terms of the number of eggs laid and hatching larvae, as well as in theirmorphology.