Identification And Function Analysis Of Salivary Enzymes Of Bemisia Tabaci Biotype B (Homoptera: Aleyrodidae) And Trialeurodes Vaporariorum (Homoptera: Aleyrodidae)

Bemisia tabaci (Gennadius) B biotype is a serious invasive pest in worldwide.It has been identified as the one of the 20 most serious invasive species by the International Union for Conservation of Nature (ICUN).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. In the relationship of herbivores and plant, people start to focus on the role of saliva components, such as digestion plants, spread viruse, interfer plant wound signal and degrade plant defense materials, cause plant gangrene, etc. In order to understand the mechanisms of host plant species increasing of B. tabaci B-biotype and its competition with Trialeurodes vaporariorum (Westwood), both whiteflies differences on character and function of saliva alkaline phosphatase, polyphenol oxidase and peroxidase were studied. The main results are as follows.1.Effects of host plant on the alkaline phosphatase activity in the saliva of Bemisia tabaci biotype B and Trialeurodes vaprorariorumFor understanding the role of salivary alkaline phosphatase (ALP) secreted by Bemisia tabaci(Gennadius) biotype B and Trialeurodes vaporariorum (Westwood) in their competition and substitute, ALP activities of B. tabaci B-biotype and T. vaporariorum on different host plants were studied and compared by the mass assay using pNPP as the substrate. Activities indicating that the pH optimums for ALP from both whiteflies were pH 8.2, but in the range of 7.4-9.4, ALP activities of B. tabaci B-biotype was higher than those of T. vaporaiorum.The order of ALP activities of B. tabaci B-biotype and T. vaporaiorum on different host plants was cabbage>cotton>tomato>celery and celery>tomato> cotton>cabbage, respectively. Therefore, we could see salivary ALP was relative with the different addiction of whiteflies on host plants. The salivary ALP activities of B. tabaci B-biotype and T. vaporaiorum on the same host plants were significantly difference. On cabbage, salivary ALP activity of B. tabaci B-biotype was 98.53±5.70 (OD/min·mg), significantly higher than that of T. vaporaiorum;ALP activies secreted by B. tabaci B-biotype from cotton and tomato were 3.30 and 2.24 folds higher than those of T. vaporaiorum, respectively; However, ALP activities of B. tabaci B-biotype and T. vaporaiorum collected from celery, were 55.93±2.39 and 36.38±3.42 (OD/min·mg), respectively. It was assumed that ALP could help whiteflies to adapt different plants and B. tabaci B-biotype might have stronger ability than T. vaporaiorum in utilizing the enzyme to metabolize and absorb nutrients 2. Identification and function analysis of polyphenol oxidase and peroxidase in saliva of Bemisia tabaci Biotype B and Trialeurodes vaporariorumInherent superiority in using salivary phenol oxidising enzymes were explored to explain invasion of whitefly. Bemisia tabaci biotype B.Sucrose liquid diets and sucrose-agarose gels were used to study two oxidoreductases, polyphenol oxidase(PPO) and peroxidase (POD), in the saliva of B.tabaci and its congener in invaded areas, Trialeurodes vaporariorum.Activities indicating the presence of these two enzymes were found. Both enzymes were present in the gelling saliva and watery saliva of the two species.The PPO and POD activities in watery saliva of B. tabaci were 2.27 and 1.34 folds higher than those of T. vaporariorum on tomato.The PPO and POD activities in watery saliva of B. tabaci on cabbage were 1.54 and 1.65 folds higher than those on tomato.After feeding on tomato plants, which had been pre-treated with pathogen(Phytophthora infes(?)ans) infection, mechanical damage, whitefly feeding or exogenous salicylic acid, PPO activities in watery saliva of B. tabaci increased 229%,184%,152%, and 139% in response to the four treatments while those of T.vaporariorum only increased 133%,119%,113%,103%.respectively.The PPO was secreted in their saliva and reacted with a range of phenolic compounds. PPO activities of B. tabaci were 1.82-6.20 folds higher than those of T. vaporariorum when five phenolic compounds were added to the liquid diets and used as substrates. As most of these phenolics occur naturally in plants and are involved in plant induced resistance, it was assumed that B. tabaci has stranger abilities than T. vaporariorum in utilizing enzymes to overcome induced resistance and modifying plant's phenolic composition. The importance of the PPO and POD, secreted by B. tabaci and T. vaporariorum,in their host adaptation, competition and replacement is discussed.