A factor reducing cocoon filament quality in silkworm reared on an artificial diet during all instars

Abstract

It is known that filament quality of cocoons of the silkworm reared on an artificial diet during all instars is worse than that of the silkworm raised on mulberry. To solve this problem, the polyphagous strain “TN32×TC60” was compared to the commercial strain “N124×C124” reared on two kinds of diets. Certain factors were shown to reduce the cocoon quality, for example, the filament size and shape. When the silkworms were reared on mulberry, the reelabilities of N124×C124 and TN32×TC60 were 87 and 66%, respectively. In both strains, the shape of the filaments, spinet and the water content of the silkgland were normal. When both strains were reared on an artificial diet, the reelabilities decreased and the cocoon filaments became thinner. The filament shape did not change in N124×C124, but in TN32×TC60 the shape was extremely flat although the spinet shape was normal. The anterior-middle part of the silkgland contained more water than in silkworms raised on mulberry in both strains. These results suggest that the filament size and the flat shape were factors in reducing reelability. They would be influenced by water content, and not by the shape of the spinet. We assumed that artificial diets affected the water content of liquid-silk because filament quality and water contents were improved by rearing on mul-berry only during the 5 th instar. Practically, we believe that the filament shape is suitable for the index of the polyphagous strain breeding because the flat filaments can be removed by breeding.