| Bemisia tabaci (Gennadius) B-biotype is an important world wide insect pest. In many districts, the alien B-biotype has been displacing indigenous non-B biotypes. B tabaci B-biotype invaded in China in the late-1990s and has been causing serious economic losing in vegetable and ornamental products since then. Trialeurodes vaporariorum (Westwood) is also a major pest of vegetables and flowers. Usually both whitefly species co-exist in many vegetables and ornamentals in northern China and the displacement is frequently observed between them. In order to clarify the relationships between the two whitefly species, the population competition, reproductive disturbance and biological characteristics were evaluated in greenhouses and controlled conditions.Our results indicated that B. tabaci B-biotype had the ability to displace T. vaporariorum on tomato plant at controlled greenhouse conditions (23.6℃). When both whitefly species co-existing at the initial population rates (sex ratio was 1:1) of 20:10, 15:15 and 10:20, B. tabaci B-biotype completely displaced T. vaporariorum after four, five and seven generations, respectively. During both whitefly species co-existing, the population of B. tabaci B-biotype increased respective 13.4, 12.4 and 17.0 times, however, that of T. vaporariorum decreased sharply instead of increasing. When developed solitary on tomato plants for successively seven generations, the population or B. tabaci B-biotype grew much faster than that of T. vaporariorum, 10.9 vs. 4.7 times. Moreover, the rates of female individuals in the population of B. tabaci B-biotype were 1.62 for solitary population and 1.69 for co-existing, higher than those of T. vaporariorum, 1.20 and 1.43, respectively.Field investigation indicated that B. tabaci B-biotype could disturbance the mating behavior between male and female individuals of T. vaporariorum. Further video monitoring stated that courtship behavior could happen between both whitefly species; however, no mating action was conducted. Male B. tabaci B-biotype individuals paid 6-13 times of courts to female T. vaporariorum, while male T. vaporariorum seldom paid court to female B. tabaci B-biotype. During a three days observation, the pre-period of mating shortened and mating frequency increased when three male B. tabaci B-biotype or one male T. vaporariorum individual presented; however, there were no significant differences compared with those of one female and one male pairs. Furthermore, there were no differences between day and night when the mating rhythm of both whitefly species compared. The developing periods from egg to adult emerging of B. tabaci B-biotype were shorter (21.2, 24.3 and 26.6 d, respectively) than those of T. vaporariorum (22.1, 28.7, 30.2 d) when tomato, tobacco and cotton as the host plants, respectively. There were no significant differences between solitary and co-existing populations of B. tabaci B-biotype or T. vaporariorum when developing period of pre-mature were tested. The fecundity (251-278 eggs) of B. tabaci B-biotype was greater and the lifetime (29.6-30.8 d) was longer than those of T. vaporariorura (54-74 eggs, 27.8-30.8 d), no matter the B. tabaci B-biotype was solitary population or co-existing with T. vaporariorum.Our results indicated that B. tabaci B-biotype can displace T. vaporariorum at certain conditions. Although male B. tabaci B-biotype individuals can pay court to T. vaporariorum females many times, they can not disturb the mating behavior between male and female pairs of T. vaporariorum. The more powerful ability of population growing (2.32 times), greater reproducing ability (3.76-4.65 times), higher sex ratio and shorter developing period of B. tabaci B-biotype may explain the displacement of T. vaporariorum by B. tabaci B-biotype.
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