Comparative Effects of Glycine max and Glycine soja Leaves on Clanis bilineata tsingtauica Rearing Performance

In China, the substantial gap between domestic soybean supply and growing consumption necessitates large-scale soybean imports. The use of cultivated soybean (Glycine max) leaves as feed for the edible insect Clanis bilineata tsingtauica reduces crop yield, posing a threat to national soybean production security. To address this issue, this study evaluated wild soybean (Glycine soja) as a potential alternative feed source. Comparative analyses examined the nutritional and anti-nutritional properties of G. max (cv. Qihuang34) and a laboratory-preserved G. soja germplasm, together with their effects on larval growth performance, nutritional composition, and associated microbiota. G. soja leaves exhibited significantly higher crude fat (5.61% vs. 2.17%), ash (11.07% vs. 9.62%), neutral detergent fiber (23.75% vs. 21.00%), calcium (4.05 g/kg vs. 3.41 g/kg), and phosphorus (2.52 g/kg vs. 2.38 g/kg) than G. max leaves, along with lower trypsin inhibitor levels (p < 0.01) despite higher phytic acid content (p < 0.05). Fifth-instar larvae reared on G. soja leaves showed a 12.9% greater body weight (6.846 g vs. 6.066 g), higher crude protein (672.14 g/kg vs. 555.02 g/kg), total soluble sugar (21.27 mg/g vs. 8.96 mg/g), and soluble protein (26.35 mg/g vs. 24.71 mg/g), but lower crude fat (187.44 g/kg vs. 205.82 g/kg, p < 0.05). 16S rRNA sequencing revealed distinct phyllosphere microbial communities, with G. soja enriched in diverse taxa (e.g., Bacteroidota, Proteobacteria) and G. max dominated by Firmicutes. Corresponding differences were observed in larval gut microbiota, and positive correlations suggested potential microbial transfer from G. soja leaves to larval guts. Overall, G. soja represents a promising alternative feed source for C. bilineata, reducing competition with soybean grain production and supporting sustainable insect farming.