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An electron-microscopic investigation was made on hypodermal tissues of silkworms spontaneously infested by nuclear polyhedral disease, due to low temperature stress. It was established that the polyhedral virus is formed in the viroplasma produced after viral cell infection, is included in the intimate and developing membrane singly or in fascicles containing several (up to 9) and is finally incapsulated in polyhedral protein. Besides viral rods, various polymorphic forms were observed in the nucleus and around the polyhedras in the process of formation, which are considered as viral substructures (or nucleocapsidless viruses), membrane structures and surplus synthetized polyhedral protein. It can be presumed that virus replication in single cell nucleus is a continuous process which goes on until complete nuclear structure depletion.

Pathohistological changes in silkworms, spontaneously affected by nuclear polyhedry are investigated. The J-124 X C-122 hybrid after the fourth moulting is tested. After being subjected to a low temperature stress the silkworms were killed and material for pathohistological studies were taken from them. It is established that the most suitable tissues for the replication of the polyhedry virus of the silkworm were the cells of the fat bodies, the tracheal matrix and the hypoderm. Not all polyhedra form simultaneously. The virus as polyhedral bodies is detected in the infected tissues, cells respectively, on the 55th day (at the earliest) by the action of the low temperature stress. The histopathological investigation is recommended as a method for reliable and relatively early diagnoses.

Experiments were carried out with eggs of Bombyx mori of the J--124xC--122 hybrid, imported from Japan. Tested was the feeding of the silkworm moth on leaves of dandelion (Taraxacum officinale L.) up to the end of the III instar. Feeding was also carried out with dandelion leaves up to the end of the IV instar, which, immediately prior to offering to the moths were sprinkled with water solutions of flurazolidon, 1.5 per cent, chloramphenicol with propylen glycol (5%)--50 cm3 each/1 of water or nalidixic acid, 2.5 per cent. The effect was studied of the antibacterial preparations applied to every kind of feed on the amount of microflora in the alimentary tract. It was found that moths given dandelion leaves reached the III instar, however, there was a very early manifestation of spontaneous nuclear polyhedrosis and bacterial infections of the alimentary tract. The addition of antibacterial preparations reduced the outbreaks of the two diseases and the microflora in silkmoths. Discussed is the possibility of the wide use of broad-spectrum antibacterial drugs in the prevention of these diseases.

Histopathologic studies were carried out on fifth instar silkworm moths of the Super 1 x Super 2 hybrid infected orally with Baculovirus bombycis along with ultrastructural investigations of the pathogen itself. It was found that the earliest changes in the moths set in at the 60th hour post inoculation. They consisted in the aggregation of chromatin, and the formation of polyhedral bodies in the fatty body, hypodermis, and peritracheal matrix; these appeared in the glandular tissue too, but not earlier than the 120th hour, while in the hemolymph they were found at the 40th hour. The morphogenesis of the virus was followed up via the electron microscope, giving a description of its structure. It was found to replicate in the viral plasma formed in the nuclei of the infected cells. First the nucleocapsids emerged which were enveloped in a two layer outer (developing) membrane while they were in the viral plasma or in the space between it and the nuclear membrane (the so-called ring zone). Then these tended to thoroughly enter the ring zone and incorporate randomly into the polyhedral bodies. The virions were enveloped at the rate of one in the developing membrane, rarely being up to five per envelope. It was assumed that both at induction and at artificial infection the process, resp., the virus replication runs its course after one and the same pattern. However, the number of virions in the developing membrane depends on the tissue in whose cells the virus is replicated.