It is well known that fine fibers separated from the cocoon filament produced in the sericin layer of the silkworm, Bombyx mori, cocoons are the main cause of white spots (lousiness), which degrade the quality of silk threads. Due to its metric traits, which make it difficult to accurately determine the amount formed, the heritability of lousiness is complex and many of its features remain unknown.

 This paper describes a novel method for turning fine fibers separated from the cocoon filament into fine fiber assemblies (FFAs), by shaking and mixing silk filaments and fibers in a test tube. The method exploits the fibers’ tendency to tangle. A correlation was found between the number of fine fibers separated from the cocoon filament, as measured by the conventional method, and the number of FFAs, showing that the method here developed for counting the number of FFAs can be used as a simple means of measuring the number of fine fibers separated from the cocoon filament, which is necessary for selective breeding and genetic analysis.

 Fructose 1, 6-bisphosphate aldolase (EC 4.1. 2.13.; ALD) is an enzyme that is central to glycolysis and gluconeogenesis in the cytoplasm of higher organisms. In the silkworm, Bombyx mori, this enzyme exists primarily in the form of tissue-specific homotetramers BmALD2 (type-S) or BmALD1 (type-F), mainly in the fat body and muscle, respectively. In the present study, a consistently high level of ALD activity was detected in the glandula (g.) lacteola, one of the exocrine glands of the male reproductive system, which was transmitted without loss upon mating to the spermatophore formed inside of the female bursa copulatrix . The overall kinetic properties of this seminal ALD are similar to those of the previously studied type-F. In addition, reverse transcription-polymerase chain reaction analysis showed that BmALD1 was predominantly expressed in the g. lacteola. These data strongly suggest that the seminal fluid contains type-F ALD, which is a homotetramer of BmALD1, which has higher overall enzymatic activity, achieves greater rates of extracellular glycolytic output, and can support sperm maturation in the spermatophore.