Studies On The Biology And Virus-Transimission Mechanism Of The Virus-Transimission Vectors In Tobacco Field Ecosystem In Yunnan

According to the transmission and epidemiology of tobacco witches' broom disease, an important disease of tobacco in Yunnan Province, the virus-transmission characteristics and biological properties of several main transmission-mediated insect vectors, such as Myzus persicae (Sulzer), Sogatella furcifera (Horvath), Cyrtopeltis tennuis (Router), Nephotettix cincticeps (Uhler) and N. apicalis (Mots), were studied systematically. As M. persicae and C. tenuis are the dominant vectors in quantity during the life cycle of tobacco in Yunnan field ecosystem, their biological characters such as the development thermal thresholds and effective accumulative temperatures were studied, and the mean longevity and productivity as well as the mean generation stage were simulated with equation for the adult of the M. persicae. Moreover the dynamics of the populations of M. persicae and C. tenuis were surveyed from the whole tobacco plants and with the yellow trap cards simultaneously. This is the first report up to now about the result of the transmission of the phytoplasma of tobacco witches' broom (PTWB) by 5. furcifera and N. cincticeps. Furthermore, a sustainable management strategy of those virus-transmission vectors was constructed. The results are summarized as follows:1. Dynamics of the Population of Myzus persicae (Sulzer) and Cyrtopeltis tennuis (Router).M. persicae and C. tennuis were collected from yellow sticky traps and the whole tobacco plants in the fields of Weishan and Yiliang counties. The spatial distributions of M. persicae on the whole tobacco plant and at various parts of a single tobacco plant were determined. The results showed that all of them were clumped as indicated with Taylor's power law; all b values were significant more than 1. Quantitative way has been used to analysis the confounding effects of various ecological environments to M. persicae. Covariance analyses showed no significant differences between the coefficients from the two experimental locations and from different parts within a tobacco plant. Significant correlations were found between the M. persicae densities on the yellow sticky traps and on the tobacco plants in the different experimental locations. Using improved Wilson's equation could be used in the field to estimate M. persicae densities quickly. Field survey results indicated that there were more numbers of Aphids in Weishan, but the amounts of M. persicae had no significant difference among 5 directions. In year 2000, Pterous and Apterous aphids per tobacco plant had significant difference (F=12.98, P<0.05, df=1,32 in Weishan; F=10.87, P<0.05, df=1, 22 in Yiliang). And the quantities of Aphids collected on yellow sticky traps and from tobacco plants showed little significant correlation. The population dynamics of C. tennuis vary in different year, but the amounts of C. tennuis had no significant difference among 5 directions. And density of C. tennuis has positive relationship with incidence of tobacco witches' broom disease.2. The mechanism of insect vectors transmission of tobacco witches' broom.Transmitted by green peach aphid, Myzus persicae (Sulzer). Virus could be transmitted to each isolate of PTWB from Dali, Honghe and Kunming counties by 3 pieces of adult insect M. persicae. The efficiency of transmission was duplicate when 5 adult aphis were inoculated to each tobacco plant. And the maximum transmitting efficiency was achieved if the inoculated amount of adults was more than 10 per plant. M. persicae could transmit PTWB with 15 min of minimum acquisition-access period, and transmitting efficiency was increased as the acquisition-access period was lengthened gradually and reached maximum with 24 hours of acquisition-access period. The minimum inoculation-access period was 7 min, and transmitting efficiency increased gradually according to the lengthened inoculation-access period, and the maximum value obtained when inoculation-access period was beyond 12 hours. However, no matter how long the virulence-acquisition was, 24 hours following the acquisition-access period w...