Preliminary Study On Resistant Effects Of Silkworm By Different Environmental Factors And Microorganisms

Silkworm, like other insects, its intestinal tract is a complex microecosystem which resides with abundant microorganisms. These organisms play important roles in the host defense against pathogenic microorganisms, food digestion and the promotion of immune system, and so on. Silkworm, as a model for Lepidoptera, is an important economic insect, it is necessary to investigate the intestinal microecosystem of other Lepidopters, control the pests of crops and other aspects. Meanwhile, the external environment factors, such as food, temperature, have an effect on the physical health of the silkworm larvae, and the instability of physiological resistance of silkworm will in turn affect the balance of gut microflora. Bombyx mori sick blood-type septic disease caused by Bombyx mori nuclear polyhedrosis virus (BmNPV) is a subacute disease which influences sericultural development. Its outbreak will cause widespread epidemic disease. Therefore, knowledge of different environment factors which influence the acetylcholinesterase activity of silkworm and the relationship of intestinal dominant bacteria with BmNPV will provide strategy for further studying the interaction between host and pathogen.In this study, we explore the effects of different environment factors on acetylcholinesterase activity and lipase-producing strains isolated from the silkworm reared on different forages against infection rate of BmNPV. Besides, we perform a plot test for strains'security.The results are as follows:1. Environmental factors had significant roles in the physical health of silkworm. The acetylcholinesterase activities had no difference in different varieties of silkworm, and the activities increased with the silkworm larval instars. At low temperature (15℃), the instars of silkworm prolonged and the acetylcholinesterase activity was stable; on the contrary, at high temperature (35-40℃), silkworm's resistance became weak, the mortality increased, and the acetylcholinesterase activity was higher. Organophosphorus pesticides could reduce the silkworm's resistance, and acetylcholinesterase activity would gradually decrease.2. Testing the effect of isolated strains on infection rate of BmNPV, the results showed when the silkworm larvae were reared with mulberry leaves added on bacterial fermentation broth, BmNPV infection rates had different degree of lower compared with the control group. Among these strains, the discrepancy of endophyte SWB8 was significant compared with the controls.Detecting infection rate of BmNPV after silkworm reared with mulberry leaves added on different combinations of bacterial fermentation broth SW41, SW80, SW82 and SWB8, respectively. The results indicated that each combination had a different degree of lower against BmNPV infection rate. The effect of combination SWB8 and SW82 was best, and the discrepancy was significant. However, the experiment needs to be repeated, because the standard error of this combination is too high.3. We found that there had no side effect on silkworm's health, cocoon and disease resistance in the experiment of freeze-dried bacteria powder's security. We also exploit microecological preparation of these strains, because of the higher prime cost and the longer production cycle, it will need more explorations in addition.