Anatomical changes of the beetle digestive tract during metamorphosis correspond to dietary changes

During pupation, the tissues of holometabolous insects change in preparation for the adult lifestyles, although little literature exists examining this hidden process in detail. Using beetles as a model, we hypothesized that species where the adult and larva have the same diets will show less pronounced changes of the digestive tract during metamorphosis than species where the adults diets differ. We also wanted to observe these changes and document them at a level of detail missing from the current record. We compared the structure of the digestive tracts of scarab beetles Oryctes rhinoceros, Thaumastopeus shangaicus, and Protaetia spp. (Coleoptera: Scarabaeidae)-where the larvae eat wood, soil, or compost while the adults feed on soft plant matter, tree sap, and rotting fruits-with the tortoise beetle, Cassida circumdata (Coleoptera: Chrysomelidae), which feeds on leaves as both larva and adult. In the scarab beetles we observed considerable changes in the digestive tracts during the pupal stage, which we could divide into distinct stages, while in the leaf beetle pupae, the gut did not change. This information can provide new insight into metamorphosis, and the illustrations of what occurs during pupation are novel contributions to this field that will facilitate future work.