The focus of this article is to trace the history of the etiology of flacherie from the middle nineteenth century to the decade of the 1960s. In 1867, Louis Pasteur ascribed the pestilential epizootics among silkworms to two symptomatically different diseases, pebrine and flacherie. Identification of several bacteria and viruses as the pathogens of flacherie has led to the modern concept of flacherie as follows: a complex of silkworm diseases that differ in etiology but share the common sign of flaccid condition. The conceptual innovation entailed fundamental changes in the approaches to nosology and diagnosis. The viral pathogens have greater potential than the bacterial ones for catastrophic losses in sericulture because they are obligate parasites, highly virulent and persist in the sericultural environment long enough to allow year-to-year infection cycle. Until the end of the nineteenth century, scientific research on flacherie was conducted almost entirely in Europe. At the turn of the century, however, Europe was slowly being overtaken by Japan as a leading center of flacherie research.

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Resistance against Bacillus thuringiensis (Bt) toxin Cry1Ac in Bombyx mori is controlled by a resistance gene that is expressed dominantly. We developed a segregation model and determined the linkage group using linkage analysis with amplified fragment length polymorphism (AFLP) and single-nucleotide polymorphism (SNP) markers. We used the BF₁ progeny produced by crossing female F₁ (resistant c440 × susceptible N28) with male N28 strain, because no crossing over occurred in the female silkworms. To determine the segregation model, we screened c440, N28, F₁, and BF₁ by inoculating them with the commercial biopesticide Guardjet (7% Cry1Ac crystal protein). The LC₅₀ value of c440 was 221.87 mg/ml, which was 2,017 times higher than that of N28 (LC₅₀: 0.11 mg/ml). The LC₅₀ value of F₁ was 2.47 mg/ml, which was lower than that of c440 and higher than that of N28, indicating that this resistance mechanism is controlled by a resistance gene that express dominantly. For linkage analysis, we selected the Cry1Ac resistant BF1 individuals from two batches with the treatment of 3.13 mg/ml Guardjet, and designed primer sets, which can distinguish genotypes of c440 and N28 by AFLP or SNPs, for each chromosome. All resistant BF1 individuals should be heterozygous for the chromosome to which the resistance gene is linked. Linkage analysis revealed that all BF1 individuals were heterozygous for only chromosome 15, suggesting that the resistance gene is linked to chromosome 15. We assigned this gene as “incompletely dominant resistance to Cry1Ac” and designated it as “Rc1ac”.

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Desiccation tolerance is a crucial factor to survive for many terrestrial animals and plants, in particular, small animals with a large surface to volume ratio. Most terrestrial living things have any structure in their bodies to regulate the water evaporation from their bodies. In order to study the moisture permeability of small biological samples, a simple method that employs the very sensitive mass sensing and temperature control functions of a thermogravimetric analyzer has been developed. It measures the weight loss due to the water vaporization through a sample fixed on an open of a capsule containing water, resulting in the evaluation of the moisture permeability. Small tissue samples (down to about 1 mm²) can be subjected to this method. The moisture permeability of some cocoon shells has been studied with this method, which shows that it can be applied not only to the comparison among different species of silkworms but also to the comparison among the local parts of a cocoon.

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Arginase is an oligometric protein that catalyzes the conversion of arginine to ornithine and urea in the presence of metal. Arginase in the silkworm, Bombyx mori, has been shown to participate in sperm maturation. In this study, we examine the enzymatic properties of B. mori arginase identified previously. The recombinant enzyme (bmArg-r) was purified to near homogeneity by ammonium sulfate fractionation, anion-exchange chromatography and gel-filtration chromatography. The isolated bmArg-r exhibits activity toward arginine in the presence of manganese ions, whereas it was unable to catalyze lysine hydrolysis. Copper and magnesium ions did not accelerate the activity toward arginine. Mutagenesis of His¹⁰⁷ in the metal-binding site of bmArg-r revealed that this residue is important for enzymatic function. We found that the mutation of His¹³², another histidine residue present in the metal-binding site, reduced the solubility of recombinant bmArg-r. It was considered that these histidine residues located in the metal-binding site of bmArg-r play a crucial role in catalytic activity.

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