Stress Resistance And Genetic Differentiation Of Bactrocera Dorsalis (Hendel)

The oriental fruit fly, Bactrocera dorsalis (Hendel), was an important invasive pest. With global warming and the frequency of trade it has a rapid spreading trend from southern to northern China. In this study, the morphology and biology study was conducted among different regional population of B. dorsalis, followed by comparing stress resistance in adverse environmental conditions. Then, the genetic differentiation of B. dorsalis was assessed by using mitochondrial DNA CO I and Cytb genes as molecular markers. The population genetic structures of B. dorsalis were revealed in terms of the natural environmental adaptability and population genetic differentiation. The study provides a theoretical basis to prevent its further spread and harm domestically. The major results are as follows:1) Comparison of morphology and biologyThe comparative results suggested difference in morphological and biological indicators of B. dorsalis among different regional populations. B. dorsalis from Guangxi population were higher than other populations in terms of the egg length, larval body length, larval body weight, pupal length and pupal weight, thereinto, an overall smallest indicators for Hubei population. Regarding the male and female adult body length, body width, wing length and wing width, the biggest female adult wing width was found in Guangdong population, followed by Hubei population. With regard to other indicators, Hubei population was higher than other populations. Fujian population was the highest regarding pupation rate, emergence rate, total fecundity and female adult longevity while there were the highest sex ratio and male adult longevity in Hubei population.2) Comparison of stress indicatorsThe average survival capacity of the four regional populations were assessed under four different stresses:water, food, humidity and temperature. With respect to tolerance of starvation and thirst by 1st day adult, Fujian population was higher in survival duration than that of the other three geographical populations, and 5th day and 10th day adults from Guangdong population was higher in survival duration than that of the other three geographical populations. The average survival duration of the adults on 1st day,5th day and 10th day were compared after treated with different conditions:with food no water> with water no food> without water and food. Comparing impact of immerging water on the emergence rate, the results showed that the emergence rate of 1st old pupae form Guangxi population was the highest than the other three populations. The emergence rate increased with the reduced immerging duration in different populations. The older pupae were, the more tolerance to drowning stress. B. dorsalis from different populations were maintained in sand with different relative water content and the results showed that 100% relative sand water content was not conducive to pupae emergence, and the emergence rate of pupae at 1st day,3rd day and 6th day from Guangdong populations were zero under the 100% sand water content condition. Under 0% sand relative water content condition, the emergence rate of 3rd day pupae was higher than 6th day pupae form Hubei population, while the emergence rate of 6th day pupae was higher than 3rd day pupae from the other three populations. The emergence rates were maintained at a higher level when treated with a relative water content at approximately 20%-60%. The tolerance to drought stress was stronger than to high-humidity stress in pupae. Comparing impacts of high temperature and low temperature on the emergence rate, the results showed that the emergence rate of 6th day pupae is higher than 3rd day pupae under the same stress. The emergence rate of 1st day pupae form Guangxi population is the highest and Hubei population is the lowest under the heat stress of 41℃. In the study of the variation of supercooling point (SCP) at different developmental stages of B. dorsalis in different parts was examined. The results indicated that the SCP of B. dorsalis varied significantly among individuals. The SCP of pupae are the lowest. The SCP of pupae from Fuzhou population is -21.1℃, the highest in Guangxi Nanning is -17.2℃.3) Genetic differentiationThe genetic differentiation of different regional population of B. dorsalis was assessed. For insects from Southern China of Guangdong, Guangxi, Hunan, Yunnan, Fujian, Anhui, and Hubei Province, mitochondrial DNA COⅠand Cytb genes were used as molecular markers for genetic differentiation analysis about and a molecular phylogenetic tree was constructed by using Unweighted Pair Group Method with Arithmetic mean (UPGMA) methodologies. In the molecular phylogenetic tree,1000 bootstrap Bootstrap re-sampling statistical method were used for each node to evaluate the confidence level of branches. The results indicated that there was a certain degree of genetic differentiation among the eight populations, but still a relatively low level.Combining with comprehensive studies of B.dorsalis, we propose the following aspects in terms of invasion mechanism of B.dorsalis:1st, adapt to the environment quickly and robust stress resistance; 2nd, genetic differentiation quickly; 3rd, a wide range of hosts; 4th, reproduce rapidly; 5th, strong competitive ability.