Dietary Supplementation with a 3-Selenoureidoindole Derivative Enhances Thermotolerance and Modifies the Hemolymph Amino Acid Profile in Silkworm (Bombyx mori)

The high bioavailability and low toxicity of organic selenium underscore its potential for nutritional fortification. This study investigated the biological effects of a novel 3-selenoureidoindole derivative (3-SeU-Ind) as a dietary selenium source in the invertebrate model organism silkworm (Bombyx mori). When reared on natural mulberry leaves, supplementation with 3-SeU-Ind (4–400 mg/L) had no significant effect on larval weight, pupal weight, or cocoon production performance. However, under compound diet conditions, the highest concentration (400 mg/L) significantly reduced both larval and pupal weights. Selenium was effectively accumulated in larval tissues and the pupal body. Under high-temperature stress, supplementation with 3-SeU-Ind (100 and 400 mg/L) significantly enhanced silkworm survival, which was associated with the upregulation of key antioxidant genes, including MnSOD, CAT, GPX, and TrxR. Furthermore, the supplementation altered methionine and lysine levels in the hemolymph in a sex-specific manner. Thus, 3-SeU-Ind demonstrated potential as a safe and effective selenium supplement.