• Journal of Sericultural and Entomological Science
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• v.40 no.1
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• pp.52-59
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• 1998

For the construction of plasmid and bmNPV sarrying the FRT recognition site for the FLP recombinases, we synthesized the wild type FRT dligonucleotides. The target FRT sequences consist of three 13bp repeated DNA sequences; two repeats in a direct orientation and one inverted relative to the other two. In addition, there is an 8bp spacer region between the repeats which determune the orientation of the FRT recombination site. In order to place the FRT site both in target BmNPV genome and the transfer vector, we constructed a plasmid, FRT site both in the target BmNPv genome and the transfer vector, we constructed a plasmid, pFRT$\beta$-gal, carrying the FRT sites within the cloning sites of pSV vector and a recombinant BmNPV, vFRTPH, carrying the FRT sites at a downstream of polyhedrin promotor, respectively. In order to test the functionality of the FLP/FRT site-specific recombination system, vFRTPH, pFRT$\beta$-gal and pHsFLP DNA were co-transfected into BmN-4 cells. The resulting recombinant virus was designated a vFRT$\beta$2-gal. From construction analysis of the vFRT$\beta$2-gal with PCR technique it was concluded that the entire pFRT$\beta$-gal plasmid with $\beta$-galactosidase gene and origines of replication flanked by two functional hybrid FRT sequences. The efficiency of recombination was 8.7%, which was higher than that(2.2%) of recombination between a conventional transfer vector and the wild type BmNPV.

• International Journal of Industrial Entomology and Biomaterials
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• v.4 no.1
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• pp.43-49
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• 2002

We have cloned cDNAs encoding toxin from the spider, Araneus ventricosus, and constructed a recombinant baculovirus expressing the insecticidal toxin. The cDNAs encoding toxin were cloned from the cDNA library of A. ventricosus. Sequence analysis of the cDNAs encoding the toxin of A. ventricosus revealed that the 240 bp cDNA for AvTox-1 and 192 bp cDNA for AvTox-2 have an open reading frame of 80 and 64 amino acid residues, respectively. The deduced protein sequence of the toxin genes of AvTox-1 and AvTox-2 was aligned to that of the snack Anemonia sulcata and scorpion Centruroides limpidus limpidus, respectively. Northern blot analysis indicated that AvTox-2 toxin gene showed a fat body-spe-cific expression pattern at the transcriptional level. Furthermore, we have explored the possibility of improving baculovirus by incorporating the A. vontricosus toxin gene into Bombyx mori nuclear polyhedrosis virus genome under the control of polyhedrin promoter, The AvTox-2 toxin gene was expressed as approximately 5.8 kDa band in the recombinant baculovirus-injected silkworm larvae. Bioassays with the recombinant virus expressing AvTox-2 on 5th instar silkworm larvae demonstrated a decrease in the time to kill $(LT_{50} days)$ compared to wild-type BmNPV-Kl $(LT_{50} 6.72 days)$ in the injection of 10 viruses. These results indicate that A. ventricosus toxin is a novel member of the spider toxin family, suggesting that the toxin gene can be used in recombinant baculoviruses to reduce insect feeding damage and increase the speed of insect kill.

• Current Research on Agriculture and Life Sciences
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• v.15
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• pp.69-81
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• 1997

For the prevention of worldwide prevalent disease of nuclear polyhedrosis virus (NPV), environmental conditions and their incidence of grasserie was investigated through 57 cases of silkworm rearing from the year of 1979 to 1993 in the countries of Korea, Japan, and Philippines. Relationship between the occurrence of NPV and environmental factors were also analysed from the aspect of causal pathogenesis. Unfavorable foactors related to the prevalence of NPV disease was reconfirmed by the assay of experimental rearing. Silkworms reared on mulberry leaves or artificial diet appeared similar result on the occurrence of grasserie. Disinfection by formalin and simple sweeping or washing was not significantly different on the occurrence of NPV disease. Following insufficient ventilation on the younger larvae. from the 1st to 3rd instar, the disease by NPV at the later stage was remarkably emphasized those insidence. An experimental rearing from 1993 to 1996 demonstrated the prevention of NPV disease by simple cleaning of sweeping under the condition of air forced ventilation, the customal practice of disinfection with formalin or any other chemical agents could be omissible.

• Journal of Sericultural and Entomological Science
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• v.27 no.2
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• pp.20-27
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• 1985

This study was carried out to investigate the histological changes after the infection of nuclear and cytoplasmic polyhedrosis viruses(NPV, CPV) and the resistance to the viruses in various varieties of the silkworm fed on artificial diet. The results obtained were as follows; Among four varieties of silkworm tested, Jam 107$\times$Jam 108 was more resistant than the other varieties tested and Jam 119$\times$Jam 120 was the most resistant to CPV. In case of peroral infection with NPV, Jam 107$\times$Jam 108 showed lower mortality than the remained varieties in low concentration (104/ml). However, all varieties showed high mortality as the concentration of viruses was increased. With infection of CPV, the varieties showed high mortality at the concentration of 107 and 108/ml, while Jam 119$\times$Jam 120 showed the lowest mortality at virus concentration of 104/ml. The fat bodies, epidermal cells and tracheal epithelial cells showed high susceptibility to NPV to break the cells completely and liberate the debris to the body cavity. The CPV infected only the cylindrical cells of mid-gut and formed polyhedrons. In some cells, CPV was liberated to gastral cavity. In the electrophoretic pattern of hemolymph protein of silkworm larvae infected with NPV, bands were dimmed and disappeared as symptom aggravated after infection. Electrophoretic pattern of homolymph proteins of silkworm larvae infected with CPV showed no numerical difference at the later stage of infection, and one or two bands was observed along with lowering the concentrations.

• Journal of Sericultural and Entomological Science
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• v.9
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• pp.67-87
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• 1969

1. Objectives and Importance. Many silkworms have been damaged by nuclear polyhedrosis virus diseases thoughout the country every year causing a decease in cocoon production by approximately ten per cent per year. The damage caused by the infections virus has occured in spite of complete disinfection. In this respect, it is well known it is impossible, at the present time, to protect the silkworm from these virus infections through chemical and physical control methods. Therefore, this author has attempted to solve this urgent problem from the view point of heredity and breeding, discovering the different resistances and heritabilities among 120 stains collected from throughout the country, and selecting the ones with highest resistance for the basic materials in the silkworm breeding. 2. Results of work 1) The strains with strong resistance to the nuclear polyhedrosis virus diseases are N$_4$, N$\sub$15/, N$\sub$48/, C$\sub$55/ and Em. the log ED$\sub$50/ values of them vary between 0.799 and 1.611. The susceptible strains are N$\sub$20/, C$\sub$62/, N$\sub$76/, N$\sub$79/ and C$\sub$108/, the log ED$\sub$50/ values of them vary between 5.159 and 7.258. (Reference Table 4) The Japanese strain with a log ED$\sub$50/, value of 3.770 is the strongest, followed by the Chinese strain with a log ED$\sub$50/ value of 3.564. The weakest is the European strain with a log ED$\sub$50/ value of 3.3381. The direction coefficient of the regression equation of the susceptibility varies between 0.1 and 0.6, the uniformness of the resistance of the preserved strains of this country is comparatively low. The hereditary henomena of the resistance of each strain and the conerete method of its application for silkworm breeding main the subjects for later studies. 2) The content of water and ash in silkworm has not been correlated with the capability for resistance to the virus diseases(Reference. Table 8). but it is very significantly correlated with mortality rate (in common reaning). In the case of the silkworms which have just completed the fourth moulting the content of water and ash is not related to the mortality rate. In the case of the silkworms which have just completed the third moulting, however, the water( +0.326) and ash (+0.362) registered a high significance. The ash content in the first ($\div$0.520) and second ($\div$0.386) moults is highly significant but water content in both cases is not significant (Reference Table 7). 3) The No. 205 strain proved to be the best in character among the various F$_1$ hybrids. No. 204 was very good in strength but a little lower in cocoon character than the control. No. 212 was a little low in coccon character and mortality was average, but the cocoon harvest was the best among all the varieties offered for (Reference Table 9). 4), In short, the above mentioned strains which are known to have strong resistance to the virus disease are expected to provide basic data for breeding strong varieties. It is proposed that continued research should be conducted on the characteristics of various strains for a satisfactory preservation of various characteristics.research should be conducted on the characteristics of various strains for a satisfactory preservation of various characteristics.