Cry1Ac-transgenic Populus × xiaohei Disrupts Digestive Physiology and Energy Homeostasis to Impair 20E-Dependent Molting in Hyphantria cunea Larvae

Plant-delivered Cry proteins effectively control lepidopteran pests, but how midgut injury develops into systemic metabolic and developmental dysfunction remains unclear. Here, fourth instar Hyphantria cunea larvae were fed wild-type (WT), pair-fed wild-type (PF-WT), or Cry1Ac-transgenic Populus × xiaohei leaves. Cry1Ac-transgenic leaf feeding impaired nutrient utilization, growth, survival, and development, disrupted the chitin-associated midgut interface, and reduced α-amylase and lipase activities. Metabolites altered relative to both controls were enriched in glycolysis/gluconeogenesis, pyruvate metabolism, the tricarboxylic acid cycle, and starch and sucrose metabolism. These changes were accompanied by reduced glycolytic activity, ATP content, and adenylate energy charge, increased AMPKα phosphorylation, reduced S6K and 4E-BP phosphorylation, and altered 20E biosynthesis, signaling, and chitin synthesis. Exogenous 20E partially restored molting-related gene expression, epidermal chitin, molting success, and developmental timing, but not feeding or growth. These findings support a proposed digestive–metabolic–endocrine model associated with Cry1Ac-induced molting impairment.