| Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) B-biotype is a key pest of greenhouse vegetables, ornamental crops and cotton in many regions of the world and an alien invasive species in China. The host plant species of B. tabaci B-biotype has been increasing with the spreading of its invaded areas. Further, in some areas such as north China, the competition between B. tabaci B-biotype and its co-existing, closely related species, Trialeurodes vaprorariorum (Westwood), had been observed. Alkaline phosphatases (ALP, 3.1.3.1) are ubiquitous enzymes in all organisms and known to play roles in phosphate uptake. Insect alkaline phosphatases are distributed in head, salivary gland(saliva), malpighian tube, intestine, cuticule, haemolymph, fat body, reproductive system and appendage. It may involved in the process of insect development, nerve conduction, hormone synthesis, material metabolism, diapause, caste formation in social insect, etc. In order to understand the mechanisms of host plant species increasing of B. tabaci B-biotype and its competition with Trialeurodes vaporariorum (Westwood), the kinetic properties of alkaline phosphatase from the two whiteflies in different developmental stages were studied and the activity of the enzyme from the two whiteflies were evaluated when their host plant species switched.The main results are as follows:1. Comparison of alkaline phosphatase in B. tabaci B-biotype and T. vaporariorum at different developmental stagesThe kinetic properties of the enzyme from the two whiteflies in different developmental stages were studied and compared by the individual assay and mass assay using the pNPP as the substrate. The results showed that the alkaline phosphatase activity was increasing in both whiteflies during the whole growth period and reached the highest level at the adult stage. Comparatively, the alkaline phosphatase activity in the 2nd, 3rd and 4th (pseudopupa) instar of T. vaporariorum were 2.58, 2.68 and 3.14 times that in the corresponding instar of B. tabaci B-biotype, respectively. However, at the adult stage, the enzyme activity in female and male of B. tabaci B-biotype were 1.24 and 1.26 times that in T. vaporariorum, respectively. Moreover, the enzyme activity in females of both whiteflies was significantly higher than in males. However, the enzyme activity of the alkaline phosphatase in the 1st instar of both whiteflies was not detected. The optimum pH and temperature for the enzyme activity in both whiteflies were 7.8 and 47℃, respectively. By testing the kinetic parameters of alkaline phosphatase from both whiteflies, we found that the affinity of the enzyme from the 3rd and 4th instar of T. vaporariorum were significantly higher than that from B. tabaci B-biotype of the corresponding instar, and also the protein concentrations of the enzyme from 2nd, 3rd and 4th instar of T. vaporariorum were significantly higher than those from B. tabaci B-biotype of the corresponding instars. But at the adult stage there was no significant difference between the two whiteflies in both the affinity of the enzyme and the protein concentration of the enzyme. Besides, the energy of activation (Ea) of the enzyme from T. vaporariorum adult was significantly higher than that from B. tabaci B-biotype adult. The results suggest that although the ability of B. tabaci B-biotype utilizing the alkaline phosphatase to promote the sclerotization and development during the larval stages may not as high as that of T. vaporariorum, its ability to utilize the enzyme to metabolize and detoxify the secondary(plant)substances and insecticides in the adult stage, however, is significantly higher than that of T. vaporariorum adult.2. Effects of plant species switching on alkaline phosphatase activity of B. tabaci B-biotype and T. vaporariorumThe activity of the enzyme from the two whiteflies were evaluated when their host plant species switched from tomato (an addicted host plant species of both whitefly species, also as the control), to cotton (B. tabaci addicted to and T. vaprorariorum can develop), cabbage (B. tabaci addicted to but T. vaprorariorum cannot survival) and celery (T. vaprorariorum addicted to and B. tabaci cannot survival) plants. The results showed that the alkaline phosphatase activity from both kind whiteflies could be significantly affected by plant species switching. Switching to cotton and celery for 72h the alkaline phosphatase activity of B. tabaci were decreased by 59%and 45%, while switching to cabbage for 72h the alkaline phosphatase activity of B. tabaci were increased by 14%. Switching to cotton and cabbage for 72h the alkaline phosphatase activity of T. vaprorariorum were decreased by 12%and 64%, while switching to celery for 72h the alkaline phosphatase activity of T. vaprorariorum were increased by 18%.Moreover, the alkaline phosphatase activity of B. tabaci were kept increasing after switching to tomato, cotton and cabbage, while it increased first then decreased after switching to celery. And the alkaline phosphatase activity of T. vaprorariorum increased first then decreased after switching to tomato, cotton and celery, while it was kept increasing after switching to cabbage. adult.The results suggest that the alkaline phosphatase play an important role in the host adaptation of both whiteflies and B. tabaci may have higher ability than T. vaprorariorum to utilize this enzyme to metabolize substances.3. SummaryThe alkaline phosphatase activity was increasing in both B. tabaci B-biotype and T. vaporariorum during the whole growth period and reached the highest level at the adult stage.Some kinetic properties of the enzyme from the two whiteflies were also changed during the growth period. And the alkaline phosphatase activity from both kind whiteflies could be significantly affected by plant species switching. All those results indicated that alkaline phosphatase may play a important role in the growth and host adaptation of the whiteflies. B. tabaci B-biotype may have higher ability to utilize the enzyme to metabolize substances than T. vaporariorum. And T. vaporariorum may have higher ability to utilize the enzyme to promote the sclerotization and body development than B. tabaci B-biotype. In the process of host adaptation, alkaline phosphatase may help the whiteflies to assimilate sucrose and to detoxify the secondary substances in the host plants. Moreover, B. tabaci B-biotype's response to plant species switching was faster and more effective than T. vaporariorum's.
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