Adaptability Of Bemisia Tabaci (Gennadius) To The Host Plants And Plant Secondary Substances

In Jiangsu province, Bemisia tabaci (Gennadius) can survive winter in double-layer-film-covered shelters or greenhouses. In the late spring and the early summer of following year, when the shelters and greenhouses are uncovered, adults of B. tabaci can migration between different host plants with similar or different preferences. The migration of B. tabaci usually takes place between different host plants with similar or different preference host plants. During the different growth periods of host plants, the migration of B. tabaci was also observed. Currently, however, there is little information about the mechanism of outbreaks of B. tabaci. The objective of the present study was to investigate the adaptation of B. tabaci to changing host plants, the physiological adaptation of B. tabaci during migration, and the effects of plant secondary metabolites in different host plant. These knowledge may be of crucial importance to provide a theoretical basis for explaining the adaptation and outbreak of B. tabaci .1. The effects of the migration of B. tabaci between different host plants on the oviposition and host adaptability for several generations were studied. The adults of B. tabaci were selective in oviposition among different preference hosts. When B. tabaci migrated from high preference hosts to the low preference hosts, the adaptability decreased drastically. Opposite trend was observed when B. tabaci migrated from low preference hosts to high ones. The adaptation duration was related to the difference in different hosts. After 1-2 generations, oviposition returned to the normal level of the new host plant.2. After being fed on the bridging host for 3 generations and transformed back to the original host, B. tabaci developed an ordinary adaptation. When there existed observable differences in preference between the bridging host and the original host, the bridging host may play stimulation effects on oviposition and the adaptability of oviposition.3. The activities of carboxylesterase(CarEs), Glutathione S-Transferase Agents(GST)and mixed-functional oxidase (MFO) in the adults of B. tabaci changed correspondingly as the adults of B. tabaci migrated between different preference host plants. The response time of CarEs and GST to the change of hosts was generally within 3 hours. When migrating from high preference hosts to low preference hosts, the activities of CarEs, GST and MFO increased significantly. Opposite trends were observed in the activities of CarEs,GST when the adults of B. tabaci migrated from low preference host to high preference host. The activities of CarEs and GST became stable at the 2nd generation after the migration. The activity of MFO quickly reached a stable level shortly after the migration. During the migration from bridging host to the original host, bridging host played some promotional role in improving enzyme activity of B. tabaci.4. The developmental duration and survival rate of B. tabaci were significantly affected by plant secondary substances. In an enclosed space with tomato plants as the control, the developmental duration of B. tabaci on the plants of cotton S3 and capsicum are observably longer. The differences in developmental duration were mainly observed on the 1st-3rd instar nymphs, whereas there was no observable difference on the 4th instar nymphs and pupa. The effects of plant secondary substances on the developmental duration of B. tabaci were closely related to the difference in preference between host plants. The bigger differences in the preference between host plants, the more significant effects were observed on developmental durations.5. Plant secondary substances produced significant effects on the activities of CarEs and GST in B. tabaci. The alcohol solutions extracted from the seeds and leaves of castor (R. communi L.), and the leaves of seashore mallow (K. virginica L.) were sprayed onto the adults of B. tabaci. The activities of these two enzymes in the adults of B. tabaci were determined. After 4 h of the treatment, the activities of these two enzymes were significantly higher than those in the control treatment. During the process of treatment, the activities of the two enzymes followed an upward trend. The inducing effects were also positively correlated with the dosages of solutions. The higher concentrations of the extracts were, the stronger inducing effects on the enzymes were recorded.