Metabolization of the two most abundant polysaccharides, cellulose and chitin, by an extreme generalist insect, the American cockroach

Cellulose and chitin are the two most abundant polysaccharides on Earth. To digest these structural carbohydrates, herbivorous and omnivorous insects typically rely on cellulases, while insectivorous species often express chitinases. The American cockroach (Periplaneta americana), an extreme generalist omnivore, is known to thrive on a variety of diets. However, little is known about its ability to metabolize structural polysaccharides such as cellulose and chitin. In this study, we fed cockroaches ¹³C-labeled cellulose and chitin to assess their metabolic capacity and the tissue-level allocation of these polysaccharides across sexes and life stages. Our results show that P. americana metabolized chitin at a significantly higher rate than cellulose and incorporated only chitin-derived carbon into body tissues, with clear sex- and life stage-specific patterns: nymphs allocated more chitin-derived carbon to their muscles, while females incorporated more into the fat body and reproductive tissues. These results provide in vivo evidence of P. americana's capacity to metabolize both cellulose and chitin but also reveal a strong preference for chitin utilization under carbohydrate-rich conditions. This study contributes to our understanding of nutrient allocation strategies in generalist insects and offers evolutionary insight into the digestive capabilities of Blattodea, shedding light on their adaptive strategies for utilizing a wide range of dietary materials.