The Loxostege sticticalis Linnaeus, commonly referred to as the grassland pest, is a voracious migratory pest of global significance, annually inflicting substantial economic damage on the agricultural and pastoral sectors in the Northern Hemisphere. Diapause serves as a developmental adaptation mechanism in insects to cope with adverse environmental conditions, playing a crucial role in the population dynamics and infestation patterns of the grassland pest. This study focuses on the Loxostege sticticalis, employing photoperiod manipulation to obtain larvae in five distinct states of diapause: ND, PreD, D, CT, and RD. A combined metabolomic and proteomic analysis was conducted on larvae at various diapause stages. Proteomics identified a total of 5367 proteins, including 1179 differentially expressed proteins across the diapause phases. Through Gene ontology analysis, weighted gene co-expression network analysis, and GSEA, significant proteins related to carbohydrate, amino acid, and lipid metabolism, as well as insect development, were identified. Metabolomic time-series and KEGG enrichment analysis of the five diapause stages revealed 627 significantly different metabolites, including fructose, tryptophan, lysine, and glycerol. Annotations in the protein interaction network related to ribosomal subunits 40s and 60s, which are speculated to be regulated by histone acetyltransferases and deacetylases, compressing chromatin structure and hindering RNA polymerase accessibility, thereby reducing protein-related expression. These findings expand our understanding of the regulatory networks involved in diapause in Loxostege sticticalis and offer new insights into its control mechanisms.