The relationship between yellow sticky trap (YST) captures of Bemisia tabaci (Genn.) and its parasitoids, Encarsia lutea (Masi).and Eretmocerus mundus (Mercet).and those populations measured by leaf samples (LS) was evaluated. Traps were placed in experimental fields of cotton, soybean, and eggplant at Kafr El-Sheikh district during two successive seasons 2012 and 2013. Throughout the season, the trend of increasing numbers of parasitoidson traps paralleled the increase in numbers of whiteflies. Furthermore, the numbers of whitefly and parasitoid adults captured with YST were significantly correlated with those recorded from leaf samples of the three host plants, with an exception for parasitoids on soybean during both seasons. A relatively non- glabrous soybean leaf may be a suitable texture for parasitoid searching, resulting in high number of parasitoids visited and captured by YST followed by low numbers of parasitized hosts in this crop. The highest significant numbers of whitefly and parasitoid adults were captured by YST at 60 cm above the ground (≈ top of the plant) for the three host plants over each season. Vertical distribution of eggs by whitefly females on leaves near to the top of plant and on lower surfaces gives clear evidence that females are negative to temperature and extensive light. The number of parasitoidscaught by traps was higher than those recorded by leaf samples of the three plants. This might led to low parasitism rates and consider as disadvantage of YST. Because the same trend was recorded for whitefly on the three host plants, YST could be advantage for whitefly control (i.e., trade off). Nevertheless, sticky traps placed within crops may be useful for detecting changes in whitefly parasitoid populations at a particular site and specific locations. There were significantly differences among months in numbers of whitefly and parasitoid adults captured by YST with the highest numbers trapped in September of both seasons. Thus, regular treatments of insecticide applications should be stopped at that time to give the opportunities for biocontrol agents to regulate their host population.