Studies On The Stress Resistance Of Cordyceps Spp. And The Pathogenicity Of Cordyceps Militaris To The Silkworm, Bombyx Mori

In this thesis, the latest research status about Cordyceps were reviewed; effects of ultraviolet radiation, temperature and pH on germination of Cordyceps conidiophore were studied; physiological and biochemical changes of silkworm Bombyx mori during Cordyceps militaris infection were studied. By histological section observation, the histopathology changes of the infected larvae were illustrated. The results were as follows:Studies on the effects of ultraviolet radiation, temperature and pH on germination of Cordyceps conidiophore show that the germination of Cordyceps militaris conidiophore was drastically effected by the ultraviolet radiation, and the germination of Cordyceps sinensis conidiophore was drastically effected by different temperatures. The pH values fitted to the germination of Cordyceps conidiophore are under 7, and the optimum range is 4-5.When the 5th instar silkworm larvae were infected by Cordyceps militaris conidiophore, the content of haemolymph carbohydrates, trehalose, protein and glyceride differently decreased and the decrease of haemolymph glyceride was most obvious. The activity of haemolymph trehalase also decreased in infected silkworm. The activity of haemolymph SOD, POD and CAT were changed after the silkworm were infected. From 441.841U/mLto 601.255U/mL, the activity of SOD increased most significantly in four days.The results of histological section observations implied that, in the first two days, the haemocytes of the 5th instar silkworm larvae might take a defense response after they were infected by Cordyceps militaris conidiophore, and a large amount of hyphae can't be found. The defense course could be finished in 2 days. Then, hyphae and conidiophore were found in the larval integument. There were little hyphae in other organs, but, except for malpighian tubules, most of organs were disintegrated and vacuolated. We can conclude that the toxin, which was secreted by Cordyceps militaris, may cause the death of infected larvae.