Ecophysiology Characteristics Of Bemisia Tabaci On Three Cruciferous Vegetables And Velvetleaf Control Countermeasures Research

Based on 3 kinds of brassica vegetables and abutilon those are the four of important hosts of Besimisia tabaci (Gennadius), we investigated the population dynamics of B .tabaci in the four host fields, and studied comparatively the ecological characteristic of B. tabaci in different host fields. Besides, we surveyed the revelant control strategies of B.tabaci in brassica vegetables. The main results were following:1. Based on the investigating of the population of B. tabaci in the hosts of 3 kinds of brassica vegetables and abutilon, we found that the times those the populations of B.tabaci on the four hosts studied increased to a peak were different, and so were the ranges of population wave. The order of population densities of B.tabaci on the four hosts was abutilon>cabbage>cauliflower> greengrocery. The results indicated that B.tabaci have overt nature selectivity to the host plants tested.2. Based on the investigation of distribution of each form of B. tabaci on leaves at different positions of two different host Vegetables, it showed that except that the pupa of B.tabaci are distributed on mid-underpart of host Vegetables, other forms of B .tabaci can be found in all parts of the plant, but the density is significantly different among parts. Finally the regression equation on the number of the each form of B. tabaci in each and whole part of the brassica vegetables leaves is built.3. The host preference of B. tabaci among 3 kinds of brassica vegetables and abutilon were studied in laboratory and extraventricular conditions. The results showed that B. tabaci have overt selectivity to the plants tested, they preferred abutilon most, followed by cabbage, cauliflower and greengrocery for eating and inhabiting, while preferred cauliflower most, followed by cabbage, abutilon and greengrocery for laying eggs. These test results supplied base values and theory gist for utilizing intercropping system to control B. tabaci , probing into population dynamics B . tabaci and its mechanism.4. The development, survivorship and reproduction of B. tabaci Biotype on abutilon and three commercially grown vegetables of cabbage, cauliflower, greengrocery were studied in laboratory. The total survivals from egg to adult on the four hosts were 48.53 % (cabbage),61.51% (cauliflower), 36.74 %(greengrocer)and 61.93 %(abutilon) respectively. The developmental periods from egg to adult varied from 18.23 days on greengrocery to 21.42 days on abutilon. The average longevity of adult females ranged from 17.50 days on greengrocery to 22.10 days on abutilon, while the ovipositon of B. tabaci varied from 213.33 eggs on abutilon to 110.73 eggs on greengrocery. The intrinsic rates of natural increase (rm) for B. tabaci on abutilon was the highest, followed by cabbage and cauliflower, while that on greengrocery was the lowed. According to the parameters mentioned before, abutilon was the most suitable host plant for B. tabaci in the study, which was one of the direct causes of population outbreak for B.tabaci in fields of leaf-vegetable in Shanghai.5. Based on three leaf-vegetable cabbage, cauliflower, greengrocery and abutilon as experimental materials, we analyzed the content of sugars, free amino acids and water in these four experimental host foliages, and the secretion amount and the content of sugars and free amino acids of honeydew from B. tabaci feeding on these four host foliages. The results showed that content of all the soluble sugars and the reduced sugars of these hosts were respectively different significantly. There were also some differences between the mean content of each amino acids and all the free amino acids in these experimental hosts , with some differences significant at 0.05 or 0.01 level。The daily honeydew secretion amounts feeding on the hosts tested were different at 0.01 level with each other by statistical analyses, with 0.7650mg of abutilon,1.2025mg of cabbage,0.5625mg of cauliflower and 0.3725mg of greengrocery. In addition, there were some differences among the amounts of soluble sugar, reduced sugar and all free amino acids of honeydew from B.tabaci feeding on the hosts tested, with some were different at 0.05 level even 0.01 level. The results also indicated that the host plants had effected on the amount of honeydew and its compositions secreted by B . tabaci.6. CarE and AchE activity of B. tabaci progeny fed on the different host plants were determined, and the results showed significant differences in CarE and AchE activity of B. tabaci feeding on different host plants, and the results also indicated that host plants significantly affected CarE and AchE activity of B. tabaci progeny. Among the four host plants tested, the CarE activity of B. tabaci progeny population fed on Greengrocery and Cabbage was significantly higher than that on Cauliflower and Abutilon. while it was highest on Greengrocery (3.90 times of that on abutilon). The AchE activity of B. tabaci progeny population fed on cabbage was the highest while lowest on Abutilon. There were no difference of AchE activity between Cauliflower and Greengrocery, Greengrocery and Abutilon, but the AchE activity was significantly higher in cabbage population than in other populations of B. tabaci progeny. The AChE OD values of B. tabaci progeny fed on cabbage, Cauliflower and Greengrocery were 2.85, 2.39 and 1.07 times of that on abutilon respectively.7. The experiment was conducted to estimate the economic injury level(EIL)and economic threshold(ET)of B.tabaci.Based on the integrated index of B.tabaci densities and host -stages,the regression model between infection densities of the B.tabaci and ratio of yield loss at different stages was established , that was , Y=0.824+1.783X(seedling), Y=-3.784+2.231X(rosette). The dynamics economic thresholds(ET)were proposed.