The Biodiversity And Ecological Bases Of Sustainable Control Of Dendrolimus Punctatus By Beauveria Bassiana

In this dissertation, the biodiversity and ecological bases of sustainable control of Dendrolimus punctatus by Beauveria bassiana were studied. Twelve experimental plots (14hm2 each) treated inoculatively with B. bassiana at different doses and frequencies and 1 experimental plot (20hm2) treated with chemical insecticide were set up for evaluation of suppression efficiency against D. punctatus by the two different application strategies. Investigation revealed that the population of D. punctatus in the 12 plots kept low in recent 5 years, and the highest density of larvae and percentage of trees with larvae were 0.3 larva/tree and 30%, respectively; on the contrary, the population in the plot treated with chemical insecticide fluctuated sharply, and the highest density and percentage were 21 larvae/tree and 100%, respectively.Investigation on the community of insect enemies of D. punctatus showed an abundant community existed in the plots treated with B. bassiana inoculatively. The total numbers of insect enemy species differed among development stages of D. punctatus. The number reached the peak at the stage of larva period of D. punctatus with 9 species of insect enemies, and no insect enemy was found at the stage of adult. Four species and 1 species were found in the stages of egg and pupa, respectively. The abundant community of insect enemies and temporal suppression mechanism against D. punctatus played important roles on sustainable control of D. punctatus.One hundred and seventy-four insect cadavers were collected in investigations on community of entomogenous fungi in the plots. Seven species of entomogenous fungi including B. bassiana were found. The large amount of cadavers maintained stability of community of entomogenous fungi. A percentage of 63.22% of total cadavers was infected by B. bassiana, and 25.86% was by Paecilomyces spp.. The community of entomogenous fungi was important to sustainable control of D. punctatus.To study dynamics of pathogen population, one of the most important factors on thestudy of epizootiology of insect disease, a selective dodine-oat medium was determined through screening as the most efficient selective medium for monitoring B. bassiana. Surveys on dynamics of B. bassiana in 12 experimental plots inoculated at different doses and frequencies showed that: 1. the inoculum density of B. bassiana surviving in pine plantations was correlated to released inoculum at the beginning of the B. bassiana release. 2. At the beginning period, the consequence of surviving inoculum densities at different niches of the plantations was litter layer>crown layer>soil layer. A month later, inoculum densities in X and Y plots, inoculated with B. bassiana twice and once one year, respectively, decreased by 44%~99%, and the inoculum densities decreased from 37.5~300g/ hm2 to 1.72-21.08g/ hm2 (1.0 1011 spores/g). 4 months later, inoculum densities in X and Y plots as well as Z plots inoculated with B. bassiana once one year ago ranged from 0.07~7.18g/ hm2. 3. The decline rate of B. bassiana surviving in the crown layer was the most rapid, and that in the soil layer was the slowest. 4. Based on the above results, inoculative method of releasing B. bassiana twice one year, with a dose at 37.5g/hm2 each time, was chosen as the best one in all 12 releasing regimes. In consideration of the annual life history of D. punctatus in Xuanzhou, it is suggested that releasing time of B. bassiana is adjusted to around late June.Host diversity index of infected cadavers indicated stability of inoculum density, and suggesting a potential of sustainable control. With the decrease of B. bassiana population surviving in the 3 layers of forest, the inoculum from the cadavers took an important role in the stability of the inoculum density in whole forest ecosystem. Host diversity index of the cadavers trended to get lower in summer and higher in autumn.The population dynamics of B. bassiana surviving in soil fluctuated regularly within the first 2 months, with a cycle of 20 days. From a long...