| Bemisia tabaci Gennadius (Homoptera:Aleyrodidae) is one of the most serious pests in more than 90 countries and districts in tropical, subtropical regions and adjacent temperate zones. B. tabaci is a genetically diverse group that includes many morphologically indistinguishable populations differing in biological characteristics, but displaying clear geographic distributions called "biotypes". The B-biotype B. tabaci has spread quickly and has shown breakouts in many areas since it invaded China in the early 1990s. The B-biotype destroys crops by phloem feeding, excretion of honeydew, induction of phytotoxic disorders, and transmission of plant viruses. Recently, the B-biotype has become a serious pest to vegetables, ornamentals, and other economic crops in China and it is displacing other indigenous non B-biotype B. tabaci. Application of pest-resistant plant strains will be one of the efficient and sustainable ways for its control, but the chemical control measures still will be necessary, particularly when it breakout. In this thesis, we studied the selectivity and fitness of the pest to 11 tomato varieties, investigated the influences of the varieties on interspecific competition and biological characteristics of pest's parasitoids, Encarsia formosa and Encarsia sophia, and evaluated virulence to B. tabaci and safety to the two parasitoids of pesticides and their mixtures with organosilicon in laboratory. The purposes of the studies are to provide scientific information for application of pest-resistant tomato varieties and natural enemies, and to the utilize pesticides reasonably and efficiently against this pest. The results of the experiments were summarized as follows:1 Bemisia tabaci's selectivity to and influence of tomato varieties (Huangtuoyuan, KT1, KT2, Hongtuoyuan, Hongyuanshuai 1, Juhongguan,903,809, 207,203, and 202) on development and survival of the pest were investigated in laboratory. Bemisia tabaci exhibited significantly different selectivity to 11 tomato varieties. The preferred varieties were Huangtuoyuan, KT1 and 202, the less preferred ones were 903, Hongtuoyuan and Hongyuanshuai 1, and the rest fallen in the category of the least preferred varieties. The developmental duration from egg to adult varied from 21.35 days on KT1 to 19.59 days on 207. The lowest survival rate of B. tabaci nymph on the same tomato variety was the 1st instar, and the highest was the 4th instar. The survival rate in the 1st instar in variety 203 was significantly higher than those in varieties Juhongguan and Hongyuanshuai 1. The survival rate from egg to adult was highest in variety 203 (83.50%), significantly higher than those in varieties Hongtuoyuan, KT1, Hongyuanshuai 1, Juhongguan,207 and 809. However, no significant differences had been found in the survival rates for 2nd,3rd,4th and "prepupa" among the tested tomato varieties.2 Life tables of B. tabaci laboratory populations on 5 tomato varieties, for which the pest had different preference, were constructed, and leaf hair densities, pH value, contents of major nutrients of the 5 tomato varieties were also measured. The longevity of B. tabaci adults was the longest,19 days, resulted from variety Huangtuoyuan, followed in order by those from KT1,809, and 203, whereas it was the shortest from 903 (13.82 days). The average fecundity of B. tabaci adults on 5 tomato varieties was highest from Huangtuoyuan, followed in order by those from KT1,903,809,203. The intrinsic rate of increase (rm) of Huangtuoyuan, KT1,903, 809 and 203 were 0.4706,0.4289,0.4115,0.3974 and 0.3435, respectively. Experimental results, in generally speaking, suggested that B. tabaci was best adapted and showed the greatest preference for Huangtuoyuan and the lowest fitness on 203 oppositely. There were obviously differences in resistance to B-biotype B. tabaci among tomato varieties. The results of characteristics of plants that affect B. tabaci's selectivity showed that Huangtuoyuan was satisfied to the selective requirement of B. tabaci.3 The development duration and parasite rate of two parasitoids, Encarsia formosa and Encarsia sophia, on 5 tomato varieties were compared. The results showed that development duration of E. sophia was significantly shorter than that of E. formosa on all 5 varieties. Tomato varieties could affect development duration of two parasitoids. The sequence of development duration of E. formosa on 5 tomato varieties from long to short was 903,809, KT1, Huangtuoyuan, and 203 (15.95 d-14.59 d), while the sequence for E. sophia was 903, Huangtuoyuan, KT1,809, and 203 (13.56 d-12.00 d). The sequence of parasite rate of E. formosa on 5 tomato varieties from high to low was 903,809, KT1,203, Huangtuoyuan (65.00%-50.42%); and the sequence of parasite rate of E. sophia on 5 tomato varieties from high to low was 809,203, KT1,903, Huangtuoyuan (53.33%-35.83%).4 The interspecific competition between two major parasitoids, E. formosa and E. sophia, and influence of tomato varieties on competition outcome were investigated in laboratory. E. formosa parasitized more B. tabaci than E. sophia did when presented alone on any of the tomato varieties investigated. When B. tabaci nymphs were exposed to both wasp species (either in combination simultaneous or one after the other), the number of B. tabaci nymphs parasitized by each individual wasp species, either E. formosa or E. sophia, was significantly decreased compared to when each wasp was presented on its own. The total mortality of B. tabaci was increased when B. tabaci nymphs were exposed to both wasp species compared to only one wasp species. Competition apparently occurred between E. formosa and E. sophia, which reduced parasitoid offspring numbers, but did not affect the biological control efficiency. Control efficiency even enhanced in some cases, particularly on variety HTY. When wasps parasitized one after the other, the second wasp could interfere with reproduction of the first through host feeding. This action was weaker in E. formosa than in E. sophia. The effect of different tomato varieties was not significant. Different tomato varieties had impact on the outcome of competition and biological control efficiency in a certain extent, however, the influence was not significantly.5 The toxicity of 5 insecticides and their mixtures with organosilicon on the adult, nymph and egg stages of B. tabaci were measured in laboratory. The results showed that Pyriproxyfen and Acetamiprid were effective to B. tabaci eggs. B. tabaci young nymphs were the most sensitive stage to insecticides; organosilicon itself also had virulence to young nymphs. B. tabaci old nymphs'sensitivity was lower than B. tabaci young nymphs; organosilicon also had virulence to old nymphs. Acetamiprid was the most effective pesticide to B. tabaci adults, followed by Pyriproxyfen, Pymetrozine. With organosilicon, toxicity of Acetamiprid to eggs, toxicity of almost 5 kinds insecticides to young nymphs, toxicity of Kungfu and Pymetrozine to old nymphs, toxicity of Pymetrozine to adults were significantly increased. Pyriproxyfen extremely reduced egg hatching rate through osmosis from the face to the back of leafs, extraordinary affect reproduction of B. tabaci.6 The safety of 5 insecticides and their mixtures with organosilicon on pupae and adults of E. formosa and E. sophia, two parasitoids of B. tabaci, were evaluated in laboratory. The highest toxic insecticides to E. formosa pupae were Acetamiprid and Kungfu, whereas the lowest were Pymetrozine and Pyriproxyfen. The high toxic insecticides to E. formosa adults were Acetamiprid and Kungfu, while the lowest toxic one was Pymetrozine in contrary. Pymetrozine and Kungfu were very toxic to E. sophia pupae, while Azadirachtin and Pyriproxyfen were much safer than them. Acetamiprid and Kungfu showed high toxicity to E. sophia adults, meanwhile Pymetrozine and Pyriproxyfen were low toxicity to E. sophia adults.The mixture with orgnicsilicon addition, toxicity of Azadirachtin to E. formosa pupae and E. sophia pupae were enhanced significantly. Toxicity of Acetamiprid, Kungfu, Pymetrozine and Pyriproxyfen with orgnicsilicon were not increased to E. formosa pupae, but increased slightly to E. sophia pupae. Orgnicsilicon didn't get any tested pesticides toxicity up to E. formosa adults and E. sophia adults.
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