| The Q-biotype was a main invasive pest in China which was more harmful th an the B-biotype, so it is imminent to screen the resistant species against Bemisia t abaci and explore economic and effective prevention methods. Based on the existin g research results at home and abroad, has studied 10 tobacco varieties against biol ogical parameters of Q-biotype, including the developmental duration, survival rates, fecundity parameters and so on, has screened the resistant tobacco varieties against B emisia tabaci. At the same time, choosing two kinds of the most common pathogen ic fungi, Beauveria bassiana and M. Flavoiride, determined the Bemisia tabaci by t he method of impregnation in laboratory and observed the infection process of Bem isia tabaci using scanning electron microscopy, in order to explore the control effici ency of Bemisia tabaci with pathogenic fungi and provide theoretical base for revea 1 infective characteristics of pathogenic fungi and its pathogenic mechanism. The m ain conclusions are summarized as follows:1. Effects of tobacco varieties against the biological parameters of Q-tabaci.Selecting 10 tobacco varieties, tested the biological parameters including the de velopmental duration, survival rate of each age, fecundity,adult longevity and life-ta ble parameters respectively, found that differences of parameters among 10 tobacco varieties against Bemisia tabaci were significant. In Guiyan 3, the duration was the longest which required 26.37d from egg to pupal eclosing, whereas the shortest on e only needed 17.77d in Yunyan 117, the developmental duration on average were 20d in the remaining varieties. The total survival rates of Bemisia tabaci from egg to adult were lower by 50% in Yunyan 85, Yunyan 117, Gexinsanhao, Guiyan 2 and CF225, the lowest was only 44.93% in Yunyan85. It showed correlation between th e fecundity per female and longevity of adults of Q-biotype in 10 tobacco varieties, longer the adult longevity, higher the fecundity. The 3 tobacco varieties of NC95, G140, G28 and Guiyan 3 were suitable for Q-biotype to breed in terms of the life-table parameters, which showed strong growth potential. On the contrary, it wasnot conductive for Q-biotype to reproduce with lower population growth rates in Yunya n85, Yunyan117 and CF225. With comprehensive analysis of effects of tobaccovariet ies to Q-biotype biological parameters, Yunyan85, Yunyan117, Guiyan2,CF225 and Gexinsanhao were resistant varieties against Q-biotype Bemisia tabaci, whereas NC9 5, G140, G28, K326 and Guiyan 3 were susceptible varieties, of which NC95 was the most sensitive.2. The virulence of M. Flavoiride and Beauveria bassiana to 1-2 instar nymphs of Bemisia tabaci.It had different degrees of pathogenic effect to Q-biotype 1-2 instar nymph by Beauveria bassiana and M. Flavoiride, M. Flavoiride showed the highest pathogeni city, the average accumulative mortality was as high as 90.3%, whereas the average mortality of Beauveria bassiana was lower by 86.7% compared with M. Flavoiride. Analysing the effects of time and dose, in all treatments, the insecticidal speed of M. Flavoiride was the fastest, the LT50 was only 5.157d, the shortest LT50 of Bea uveria bassiana was 5.367d, which showed fast death rate to Bemisia tabaci. The LC50 of M. Flavoiride in 4d and 12d after treating were 6.0×1013and 1.0×103, whic h decreased with time increasing. The LC50 of Beauveria bassiana in 4d and 12d a fter treating were shower,too. From the accumulative mortality、 LT50 and LC50, it sh owed good pathogenic effect on Bemisia tabaci nymph by Beauveria bassiana. Whe reas the M. Flavoiride Mf82 showed the strongest pathogenicity to nymphs of Bemi sia tabaci, which can be used as the preferred strains used in production. When th e concentration increased to 1.0×106spores/ml, insecticidal speed was the fastest, wh ich was different with Beauveria bassiana, then the insecticidal speed decreased wit h the increase of concentration.Therefore, It is proposed that when using conidia of M. Flavoiride strain Mf82 as effective ingredients controlling Bemisia tabaci, the optimal spore ratio concentrat ion is 1.0 ×106 spores/ml, whereas the optimal spore ratio concentration of Beauveri a bassiana are 1.0×107spores/ml～1.0×108spores/ml3. The observation of infection process of M. Flavoiride and Beauveria bassiana to Bemisia tabaci nymphs with electron microscopy.The observation of infection process of M. Flavoiride and Beauveria bassiana t o Bemisia tabaci nymphs with electron microscopy showed that the conidia prefered attaching the thinner skin section and the number of conidia on ventral section wer e higher than those on back, invaded the internal of Bemisia tabaci from interseg mental membrane、weak parts of integument folds. The whole conidia of M. Flavoi ride germinated after inoculation in 12h, which showed fast germinative rates on B emisia tabaci. It had emerged invasive structure such as germ tube after 24h, forma ted hyphae with spores geminating and invaded the internal body after 48h, and the body covered with mycelium with new sporulation after 72h, the tested insect larva e died with the body extremely wrinkled shrinkage and color of tawny. Therefore, t he virulence of M. Flavoiride may be higher and has a good applicative prospect.The conidia of Beauveria bassiana germinated in 12-24h, which was different with M. Flavoiride, time was a little lag. Similarly, hyphae formated with spores geminating and invaded the internal body after 48h, invaded internal organs and the body covered with mycelium with new sporulation after 72h which penetrated the s urface and extended. Compared with M. Flavoiride, the infection ability of Beauveri a bassiana was weaker, but it was also a kind of entomopathogenic fungi which h ad good application prospects with good controlling. |
PDF Full Text Request