Silkworms (Bombyx mori L.) accumulate 1-deoxynojirimycin (DNJ), a mulberry iminosugar, by feeding on mulberry leaves. DNJ is a potent α-glucosidase inhibitor that helps prevent diabetes. However, iminosugars are toxic to many insects. In this study, we analyzed the concentrations of three major mulberry iminosugars—DNJ, 2-O-α-d-galactopyranosyl-DNJ (GAL-DNJ), and fagomine—in the larvae of mulberry-feeding insect species (two mulberry specialists and six non-specialists), to clarify the differences in accumulation, metabolism, and excretion of iminosugars between specialists and non-specialists. DNJ and fagomine concentrations in the two Bombyx larvae were much higher than those in the other larvae. GAL-DNJ concentrations were low in all species. DNJ and fagomine concentrations in the excrements of Agrotis segetum (Denis and Schiffermüller) and Sarcopolia illoba (Butler) larvae were lower than in those of the other larvae. Further, iminosugar concentrations in the hemolymph of B. mori, B. mandarina Moore, and S. illoba larvae were analyzed. DNJ and fagomine concentrations in the hemolymph of the two Bombyx larvae were much higher than in that of S. illoba. DNJ concentrations in the whole bodies of the two Bombyx larvae decreased as they developed. Similarly, DNJ, and fagomine concentrations in the hemolymph of B. mori larvae decreased with growth.
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