Study On Biological Control Of Armand Pine Bark-weevil (Pissodes Punctatus)

The armand pine bark-weevil, Pissodes punctatus, is a species of the bark-weevil genus, Pissodes, the weevil family, Curculionidae, and the elytrm order, Coleoptera. It is a destructive vermin of bark-weevil that destroys pine trees, specifically Pinus armandi Chemical and physical methods are used predominantly at present for its prevention and control that have demonstrated some short-term outcomes, yet have failed to eliminate the root of the problem and attain sustained effectiveness. This can be traced to the fact that there are few studies on the means of biological control. Aiming at finding the approaches and methods for the biological control of the armand pine bark-weevil, this study builds on research conducted in the Zhehai State-owned Forest Farm in Huize County and Liushao State-owned Forest Areas in Xundian County. In this study, in order to provide the theoretical and experimental bases for developing the prevention and control methods of the armand pine bark-weevil, the author has, for the first time, completed the study on three aspects of the natural enemies, sex-pheromone and the volatile substance extracted from the host pine tree of the armand pine bark-weevil. The results are as follows:(1) The resources of the local natural enemies have been ascertained for the first time. The results shows that there are seven types of local natural enemies, among whom, three species are Pteromalidae, Dinotiscus armandi Yang, Rhopalicus quadratus (Ratzeburg), and Acrocormus sp., two species are Braconidae, Coeloides qinlingensis Dang et. Yang, Triaspis sp., one species is Eupelmidae, Eupelmus urozonus Dalman, and one species is Eurytomidae, Eurytoma blastophagi Hedqvist. The total parasite rate of the local parasitoid is 13.40%. The highest populations occur in the two species of Dinotiscus armandi and Coeloides qinlingdnsis.(2) The study on Scleroderma guani bred with armand pine bark-weevil lava has been applied for the first time, and it provides the basis for the biological prevention and control using S. guani against armand pine bark-weevil. The results show that, the parasitoid-host ratio has little effect on the developmental stages and the sex ratio, and have significant impacts on the parasite rate, successful parasitism rate, and the number of eggs and filial generations, especially on the number of eggs and filial generations. The experiment shows the parasite rate and a successful parasitism rate for S. guani bred with armand pine bark-weevil lava is high at the parasitoid-host ratio of 1 to 1, and more filial generations of S. guani are produced.(3) The practices of using S. guani for the prevention and control of the armand pine bark-weevil shows the parasitoid-host ratio of 1 to 1 is optimal in achieving the best search-and-find hits. During the laboratory experiment for prevention and control, the parasite rate of S. guani on armand pine bark-weevil attains the rates from 51.61% to 71.43%, and in the forests, from 22.22% to 41.67%. This proves that it is very effective to use S. guani in the prevention and control of the armand pine bark-weevil.(4) The results of the study on the sex-pheromone of armand pine bark-weevil show that the peak hours for the emission of armand pine bark-weevil sex-pheromone occurs from 19:00 to 20:00. Compared with alcohol, carbinol is a better solvent for the extraction of sex-pheromone, and the trap rates of the crude extracts from carbinol solvent for armand pine bark-weevil is 83.2%, and 71.4% for that from alcohol. Twelve types of chemical substances have been separated from the crude sex-pheromone extracts from carbinol and alcohol solvents using GC-MS analysis, respectively. The chemical structures of six types of them from carbinol solvent have been identified, so are five of those extracted from alcohol solvent.(5) The volatile substances are extracted from pine needles of the healthy pines, injured pines, and the bark on the upper and the middle trunk and used in trap experiments of the armand pine bark-weevil. The results show that the volatile substances extracted from the needles of healthy pines, and from bark on the upper and middle trunk demonstrate strong trapping effects, with the strongest found in the volatile substances from bark on the middle trunk. At the volume ratio of 1 to 15 between the volatile substances and hexane, all armand pine bark-weevil are trapped. The volatile substances from the needles, and bark on the upper and middle trunk of injured pines demonstrates antifeedant effects. At any volume ratio between volatile substances and hexane, the selective ratios of armand pine bark-weevil are all below 15%.(6) Volatile substances extracted from P. armandi are analyzed using GC/MS. The compositions of volatile substances extracted from healthy pines and the injured pines have been compared. The results show that there are 17 types of substances common in both healthy and injured pine needles, and 30 types unique in healthy pine needles and 34 in injured pine needles. Other findings are: 15 types of volatile substances in the upper bark of both healthy and injured pines, but only 10 in the bark of upper trunk of healthy pines, and 33 in that of the injured pines; and 47 types in the bark of the middle trunk of both healthy pines and injured pines, 18 in that of the healthy pines, and 19 in that of the injured pines. The analysis show the differences in the composition and their relative contents of volatile substances extracted from the needles, and the bark on upper and middle trunk of healthy and injured armand pines are the predominant reason for infestation of the bark-weevil on the healthy armand pines.