The Host Selective Behavior And Distribution Characteristics Of Bemisia Tabaci(Gennadius)

Based on three kinds of plants (cabbage, tomato and pepper), we investigated the host selective behavior and distribution characteristics of Bemisia tabaci .Besides, we studied the way of sampling and monitoring.The results were as following:The host preference of B.tabaci among three kinds of plants was studied in laboratory. The order of preference of B. tabaci was tomato>cabbage>pepper.The intrinsic rate of increase (rm) for B. tabaci on tomato was the highest (rm =0.1677), followed by cabbage (rm=0.1425) and pepper (rm=0.1263). It suggested that the population of B.tabaci is increasing. The population on tomato had the largest increase.The host leaf age preference of B. tabaci among 3 kinds of plants were studied in laboratory and extraventricular conditions.The results showed that B.tabaci have overt selectivity to the plants tested,they preferred fifth leaf on cabbage(36.18%),sixth leaf on tomato(21.21%)and forth leaf on pepper(32.59%) twelves hours later.The test in field showed that B. tabaci concentrated on the upper strata of tomato plants and cabbage plants, whereas below the middle on the pepper.The two results are the same.Eggs and 4th instars nymphs on older cabbage leaves and older tomato leaves had significantly shorter developmental time than on young leaves. The developmental time for egg to adults on middle strata cabbage plants was shorter than upper strata and bottom. But there was no significant in developmental time on tomato. Eggs on older pepper leaves had significantly shorter developmental time than on young leaves.1st to 4th instars nymphs on young pepper leaves had significantly shorter developmental time than on older leaves. The durations of B. tabaci immatures had no significant. The survival of B. tabaci on young leaves was higher than older leaves. There was no significant in percentage of survival from egg to adult stage among the three plants. Preference of B. tabaci adults for leaf age had no relationship with offspring performance. Within-plant distribution of adults, nymphs, and eggs of B. tabaci (Gennadius) on leaves of tomato plants were investigated in field. The results showed that B. tabaci can be found in all the parts of a plant, but the density was significantly different among parts. Eggs of B. tabaci mainly concentrated on the upper strata of the tomato plant (60.56%), whereas nymphs on the middle atrata (82.33%) and adults above the middle strata(84.62%). Leaves 3-4 for eggs, 7-8 for nymphs, 5-7 for adults were considered as the most convenient for sampling specific life stages of B. tabaci. Models were builted to estimate the number of B. tabaci on the whole plant according to the number of B. tabaci on the correlative leaves.Yellow sticky trap's height showed significant influence on trap catches,traps installed at the height of 40cm below tomato tips trapped significantly more B. tabaci adults when the population of B. tabaci was small. Traps installed at the height of tomato tips trapped significantly more B. tabaci adults when the population of B. tabaci was bigger. Traps installed at the height of 40cm above tomato tips trapped the least B. tabaci adults throughout the whole experiment. But traps installed at the heights of 40cm below pepper tips trapped significantly more B. tabaci adults all the time. The direction of the trap also showed significant influence on trap catches. The traps catched more B. tabaci adults when south-towords.Based on the number of B. tabaci adults in fields and which was catched by traps, the regression equation was conducted. The regression equation (y=1257.7769+0.9126x for tomato,r=0.9872,p=0.0001;y=1583.6151+2.0498x for pepper,r=0.9930,p=0.0001)descriped the relationship when traps installed at the heights of 20cm above plant tips. The regression equation (y=937.1351+0.6644x for tomato,r=0.9694,p=0.0001;y=1650.8030+0.8300x for pepper,r=0.9846,p=0.0001) descriped the relationship when traps were west-towards installed .Using geostatistics (GS) methods followed by simulation, we analyzed the spatial structure and distribution of B. tabaci (Gennadius) in a cabbage field. We also conducted a parallel analysis using traditional statistics. Results from the two analyses revealed that the spatial distribution patterns of B. tabaci (Gennadius) on cotton were aggregated; that the aggregation degree fluctuated over time. It was 0.50,0.22,0.30,0.34,0.31. The results showed that the semivariogram of B. tabaci adults could be described by spherical model and exponential model. The range varied from 3.88m～24.36 m. The isoclines maps of the adults were created by the geostatistical software with Kriging interpolation. The resulting maps gave a clear indication about the spatial patterns. It proved that B. tabaci had an aggregative distribution, too.