Joint Pathogenicity Of Bacillus Thuringiensis And Bombyx Mori Nuclear Polyhedrosis Virus To Silkworms

During silkworm breeding, it existed wide that mixed infection of pathogenic microbes resulted in worse quality and less quantity of silkworm cocoon and inhibiting sericultural development well. Silkworms was representative of Lepidopterous insect and important model creature, research of biological control on wich could provide much reference value for biological control of insects in agriculture and forestry. Bacterial poisoning and nuclear polyhedrosis often happened during silkworm breeding, and Bacillus thuringiensis (B.t)was applied in biological control most wide, however, research on joint infection with B.t and Bombyx mori Nuclear Polyhedrosis Virus (BmNPV) to silkworms was reported little yet. In order to research joint pathogenicity to silkworms, and discuss change laws of pathogenicity, providing theoretical terms for integrated control of silkworm diseases and biological control of agricultural insects, joint pathogenicity of B.t and BmNPV to silkworms, change of physiology and biochemistry and pathologic midgut and hemolymph histiocyte in silkworm were researched by using biological statistical analysis, technology of high physiology and biochemistry , and technology of optical microscope and TEM, and the main results were showed as the followings: 1. After joint infection with B.t and BmNPV, both two fastigiums of disease occurrence and two typical symptoms of disease appeared one after another; joint infection advanced time of death and fastigium of disease occurrence, increased mortality; there was no significant difference of silkworm mortality and weight of surviving silkworms between simultaneous infection, earlier infection and later infection; Joint infection decreased weight of surviving silkworms significantly, in which B.t played a more important part than BmNPV, and LT50 by 0.1 days~1.8 days; Different concentrations of BmNPV could increased virulence of B.t while 2.4×10~4,1.2×10~5 per ml B.t has synergistic action on virulence of BmNPV respectively. 2, After joint infection, activities of amylase and protease, pH in intestinal juice, alkaline phosphatase of larva midgut, and concentration of blood cells decreased more remarkably while pH and activity of CAT and SOD in larva hemolymph increased more obviously, and proportion of original blood cells decreased while that of plasma cells and granular cells increased more obviously than single infection. 3, After joint infection with BmNPV and sublethal concentration of B.t , proliferation speed of B.t was much quicker, but that of NPB was slower; Joint infection caused higher proportion of vegetative cells, but lower proportion of spores than single infection. 4, At 20 hours after infection, joint infection caused serious pathology of microvilli, endoplasmic reticulum, nucleus and mitochondria, especially of nucleus, but single infection with B.t didn't cause remarkable pathology of nucleus of midgut histiocyte, and with BmNPV it happened to endoplasmic reticulum, mitochondria and nuclear membrane. At 84 hours after infection, serious pathology of endoplasmic reticulum and all mitochondria of midgut histiocyte happened in joint infection, especially nuclear membrane cracked, and virions appeared both within nucleus and outside nucleus, and cells decomposed, however, most of pathologic cellular organs was found and virions appeared only within nucleus in single infection with BmNPV. 5, At 60 hours after infection, joint infection led to serious pathology of all kinds of blood cells, pathology outside and within nucleus was serious, many virions appeared, and cytoplasm decomposed before nuclear polyhedral body(NPB) was released, even blood cells decomposed before NPB was formed, however, after single infection with B.t, pathology of blood cells happened from outside nucleus to within nucleus, and pathology of different kinds of blood cells was different, and with BmNPV, all kinds of blood cells became abnormal, but could be distinguished, and nucleus and cytoplasm didn't decompose before NPB was released. At 96 hours after infection, joint infection led to intensified pathology of blood cells, which showed that all kinds of blood cells couldn't be distinguished, much more virions and NPBs...