Ontogenetic variability of the Siberian silk moth, Dendrolimus sibiricus

Introduction The Siberian silk moth Dendrolimus sibiricus is a major boreal defoliator whose outbreak dynamics vary with the proportion of larvae following 1-year versus 2-year life cycles, yet the physiological basis of this ontogenetic variability remains unclear. Methods We generated tissue-specific RNA sequencing datasets from male and female larvae expressing 1-year or 2-year life cycles, dissected into head, gut, and fat body tissue sets (49 libraries), and quantified life-cycle effects using principal component analysis and differential expression with functional enrichment. Results Across tissue sets, transcriptomic profiles were structured primarily by life cycle and secondarily by sex, with the clearest sex-dependent signal confined to gut tissues. The 2-year life-cycle trajectory was characterized by broad down-regulation of genes associated with growth and anabolic metabolism, and up-regulation of stress tolerance, catabolic remodeling, proteasome-related functions, and detoxification modules. Discussion In D. sibiricus larvae expressing the 2-year life cycle, transcriptomic patterns indicate that the prolonged larval development underlying this trajectory is associated with a diapause-like state, based on similarities to diapause-associated molecular patterns described in other insects. Laboratory manipulations of larval density, food deprivation, and host plant species did not induce a switch to the 2-year life cycle, suggesting that life-cycle determination depends on more complex cue integration and/or environmental history. Together, these results identify candidate molecular signatures of life-cycle state in D. sibiricus and provide a foundation for future studies of life-cycle regulation in this species.