An illustrated guide to dissection and abdominal anatomy of the yellow mealworm beetle

An unprecedented increase in the number and the size of yellow mealworm beetle (Tenebrio molitor) farms in North America and Europe has been driven, among other factors, by the demand for sustainable proteins. Insect farming offers ecologic advantages, including lower land and water use and reduced greenhouse gas emissions. As in conventional livestock farming, veterinarians are essential to maintain insect health because disease outbreaks can reduce productivity, compromise animal welfare, and cause monetary loss. Yet, the role of veterinary diagnosticians remains limited in this emerging sector because of the lack of standardized diagnostic tools and anatomic references. The autopsy of an invertebrate is a valuable tool that can, just as in any other species, serve to determine the cause of death, identify underlying disease processes, and guide herd health management. However, performing beetle autopsies is technically challenging given their small size, rigid exoskeleton, and fragile internal organs. Here, we offer an illustrated, step-by-step dissection protocol for adult T. molitor using standard laboratory equipment. Our method emphasizes an aqueous immersion approach that preserves tissue integrity, enhances visibility, and yields consistent results. We describe the abdominal anatomy of both sexes, including the digestive, reproductive, and nervous systems. Structures include 6 testicular follicles, bean-shaped accessory glands, and a spermathecal gland in females that exceeds the spermatheca in size. The abdominal nerve cord comprises 7 metameric ganglia, with caudal fusion.