A Study On Pathogenicity Of Beauveria Bassiana To Dendrolimus Fabulaeformis Tsai Et Liu

Pine Caterpillar is the general designation for species in Dendrolimus of Lasiocampidae family, Lepidoptera order. There are 27 species of the genus (including 4 subspecies) in China. The distribution of D. punctafus Walker is most widely with the most serious harmfulness in South China. D. fabulaeformis Tsai et Liu, D. spectabilis Butler, D, huashanensis Hou and D. superans Butler break out every year in pine forest of North China, among which D. fabulaeformis Tsai et Liu causes the most serious damage. The previous controlling methods of Pine Caterpillar usually were chemical controlling measures such as spraying pesticide with plane or applying smog of pesticide in forest. With the starting of Protecting Project of Natural Forest, it is of great significance to protect the forest ecological system, fend off environmental pollution and adopt biological-control technology. In this dissertation, the strains of Beauveria bassiana in the muscardine Dendrolimus tabulaeformis Tsai et Liu collected in the pine forest in Xiaguan forested area of Lingqiu County, Shanxi Province was isolated, selected in the lab to obtain the one which is infective and adapt to the forest ecological environment of northern China. This strain was cultured into purified strain. The strain was indentified to be Beauveria bassiana in Beauveria, Hyphomycetes, Hyphomyceres, Deuteromycotina. The experiments involved and the results are showed as following:1. The biological characteristics of the strain were studied. The germination rate under different temperature and humidity, the growth rate and the spore production of the strain on PDA media under different temperature were determined. The suitable range of temperature for the germination of the spore is 20-30℃ and the optimum temperature is 25±1℃; the suitable range of relative humidity(RH) is 72.5- 100 % and the optimum RH is 90 ±5 %. The suitable range of temperature for the growth of hypha is the same with that for the germination of the spore.2. Symptoms of infection of 5th instar larvae of D. tabulaeformis parasitized by B. bassiana were observed and changes in their weight and lengthdetermined. Weight and length of 5th instar larvae dropped obviously after infection treatment through suspension solution of B. bassiana spore. The infected larvae began to die from the fourth day after infection treatment and the survivals stopped eating, body became soft. Hypha of B. bassiana penetrated out of the cortex of some larvae accompanied by decreased weight and length. The body of dead larvae turned white due to the adherence of hypha and the weight dropped to the lowes point, which was only 20% to 40% of that of the uninfected ones. The length of the dead larvae further shortened and was only 50% of that of the non-infected ones at the 7lh day. The body of dead larvae finally became stiff.3. Changes in several disease-resistant physiological and biochemical indicators of 3U to 5n instar larvae of D. tabulaeformis parasitized by B. bassiana were determined.The method of spectrophotometry had been used to analyze the activity of endogenous enzymes of protective system in D. tabulaeformis parasitized by B. bassiana. The result showed that when larvae in their 3rd to 5th instars were infected by B. bassiana the superoxide dismutase (SOD) activities were significantly higher than those of the non-infected ones. The change trend appeared to rise at the first phase then drop at the last phase. The catalase (CAT) activities showed the same trend as SOD. By using polyacrylamide gel electrophoresis ( PAGE ) techniques, SOD and CAT in the body were successively determined from the first to eighth day after the larvae were infected by the fungi. The results showed that "some differences of SOD appeared in the band width and staining intensity. Meanwhile the CAT bands had slight differences in spectrum of enzyme. The band number changed from one in the early days into two in the later ones. At the same time the band width and staining intensity showed significant differences. These indicated that the infection of B. bassiana destroyed the protective system of enzymes in larvae of D. tabulaeformis. 5th instar larvae have higher resistance to B. bassiana than that in 3K and 411 instar larvae. Therefore, young larvae should be aimed as infection target when using B. bassiana. to control D. tabulaeformis.