Overwinter And Diffusion Of Bemisia Tabaci (Gennadius) In Jiangsu Region

Bemisia tabaci (Gennadius) can't overwinter in the open field in Jiangsu region. In order to survive, B. tabaci must come through the following cycle: overwinter in greenhouse, diffuse in field, reproduce and disserve in field, outbreak and overwinter in greenhouse again. The management of Bemisia tabaci (Gennadius) will be very efficient if the cycle can be disturbed at any one of these stages. In order to investigate into the development of the population of B.tabaci in field and the major influence factors, experiments were conducted on the overwinter, diffusion, selection and suitability of B.tabaci in the field.1. Low temperature stress experiments were conducted. The results indicated that when the temperature was over 0℃, B. tabaci did not die rapidly. While treated with temperatures lower than -2℃, small larvae began to die after 1h, large larvae began to die after 24h. All the eggs died after 6h when treated with -2℃. All the forms of B. tabaci, including adults, larvae and eggs, died after 6h at -4℃. It was also discovered that B. tabaci could overwinter in double-layer-film-covered shelter and in single-layer-film-covered shelter in the southern region of Jiangsu province2. When treated with a constant temperature of 28℃, it took B. tabaci 16.2d to complete one generation, 7.88% shorter than T. vaporariorum. But at 23℃, the period was 28.9d, longer than T. vaporariorum. At 28℃and photoperiod L:D=12:12, the time that B.tabaci needed to complete one generation was 1.39d shorter than T. vaporariorum, but when the photoperiod was L:D=8:16, the time was 2.09d shorter than T. vaporariorum. At 28℃and photoperiod in L:D=12:12, the survival rate of B. tabaci from egg to adult was 89.21%, significantly higher than T. vaporariorum, but when the photoperiod was L:D=8:16, the survival rate was 75.18%, significantly lower than T. vaporariorum. At 23℃the survival rate of the two kinds of whiteflies had no significant difference. The population of B.tabaci in shelter during winter was smaller than T.vaporariorum, which was possibly caused by lower temperatureWhen the two kinds of whiteflies coexisted, population competition was observed between them. At 28℃room temperature, B. tabaci gradually replaced T. vaporariorum as the dominant. When the room temperature was 23℃, T. vaporariorum gradually became the dominant population.3.Through systematic survey and spot inspection, the diffusion of Bemisia tabaci Gennadius overwintering in the protecting field was studied. The results showed that B. tabaci in Xinghua could overwinter in the greenhouse covered with double-layer film. And they started to diffuse from the uncovered greenhouse to the open field during the first and second ten days in June. The diffusion lasted 35-45d,and the diffusion distance ranged about 1000 to 1500m away from the source. The population density was negatively correlated to the distance from the source. The majority of the insects were 500m within the insect source. The population dynamic was closely related to the distances from the source. The peak of B. tabaci population at the place of 500m away from the source occurred 13d later than that at the place of 10m. Wind produced significant effects on the diffuse direction, and large barriers made a significant retardation action on the diffusion of B. tabaci.4.With the cucumber, cotton and water spinach as the hosts of insect source and inducer, the effects of host plant, distance between the host of insect source and inducer, insect population density on the diffusion of B. tabaci were studied under covered cage. The results showed that the number of B. tabaci diffused from the source was related to host preference discrepancy between the hosts of insect source and inducer. The stronger of preference of inducer host relative to hosts of insect source, the more adults diffused from the insect source. The number of adults diffused was negatively correlated to the distance between the two hosts. The stronger of host preference of inducer host, the faster of the decline rate of induced adults. The number of adult diffused was positively correlated to the population density at the insect source, but lower capacity for non-preference host was observed. More adults diffused from non-preference host than from preference host when population density was higher. The number of adults diffused is negatively to host nutrition, and the non-preference host could gain more adults than preference host.5.Through systematic survey, olfaction testing, free diffusion observation both in cage and class plates, the host selection of Bemisia tabaci Gennadius was studied. The results showed that there was obvious preference of B. tabai for hosts. It was highly preferable for plant egg, cauliflower, cucumber, and non-preferable for water spinach, celery and amaranth. The differences of host selection were also observed among different varieties belonging to the same genus. B. tabaci also had the similar ability to select the color of plants. It was not sensitive to single plant, but sensitive to the substance distilled from the leaves of the plant by ethanol, and obvious host selection was also detected. The process of sticking and sucking of B. tabaci was a key way for its host selection. The results indicated that by following the color of plant, B. tabaci reached the areas of suitable plants, and made the selection, accepted or refused the plant by sticking and sucking, finally selecting the suitable place on the leaf of suitable host.6. B. tabaci was highly adaptable to different hosts. On a new host, the development of B.tabaci could reach the normal level in the second generation; and in the first generation only small larva was affected. New hosts mainly influenced the survival rates of the small larva in the first generation.