GC-MS-Based Comparative Analysis of Compounds in Host Plants and Insect Gut Extracts

Background/Objectives: Herbivorous insects feed on plant tissues to obtain nutrients necessary for growth and development while simultaneously ingesting diverse plant secondary metabolites. Understanding the fate of these compounds during digestion is important for advancing knowledge of insect nutritional physiology and diet-associated biochemical processes. This study aimed to comparatively profile metabolites in host plants and corresponding insect gut extracts to generate insights into compound transfer and compositional changes within these systems. Methods: Gas Chromatography-Mass Spectrometry (GC-MS) metabolomics was combined with Ultraviolet-Visible (UV-Vis) quantification of total phenols and flavonoids to compare host plant tissues and insect gut extracts in three systems: fall armyworm (Spodoptera frugiperda) larvae on maize (Zea mays), desert locust (Schistocerca gregaria) on wheatgrass (Triticum aestivum), and silkworm (Bombyx mori) on mulberry (Morus alba). The analytical approach targeted semi-volatile and moderate polar compounds within the constraints of the extraction and detection workflow. Results: UV-Vis analysis revealed consistent enrichment of total phenols in insect guts relative to host plants (1.4- to 0.35-fold), while flavonoids were reduced (2- to 7-fold). GC-MS analyses showed clear separation of gut and plant metabolomes, with <35% shared metabolites and the majority unique to insect guts. Insect extracts were enriched in hydrocarbons, fatty acids, sterols, and terpenoid derivatives, reflecting extensive biochemical transformation. Sex-specific metabolite differences were observed in silkworm and desert locust guts despite identical diets. These findings show differences between plant and gut metabolite profiles, reflecting selective enrichment, depletion, and restructuring of dietary compounds during digestion. Overall, this study provides comparative metabolic data on insect-plant feeding systems and highlights the gut as a dynamic environment associated with changes in dietary metabolite composition. These findings contribute to understanding how plant-derived compounds are represented in insect gut extracts and establish a baseline framework for future studies investigating the biochemical processes underlying insect digestion and nutrient utilization.