Yellow mealworms dissected for the first time

By Martin LaSalle Jun 22nd, 2026

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In 5 seconds Working on exoskeletons of the tiny beetle under a biocular microscope, researchers at UdeM’s Faculty of Veterinary Medicine succeed in an unprecedented anatomical mapping.

Marie-Odile Benoit-Biancamano and Chloé Rosa-Teijeiro
Photo : Chloé Rosa-Teijeiro

The dried larvae of the yellow mealworm beetle (Tenebrio molitor) are comparable to beef or poultry in nutritional value but the mealworm has a far smaller ecological footprint. It was recently approved for human consumption by the European Food Safety Authority.

However, farming the insects is fraught with risk. Outbreaks of densovirus—a DNA virus that infects invertebrates—have decimated some mealworm farms. And due to the lack of diagnostic tools, no biosecurity advice is available to farmers.

“Without a precise description of the insect’s normal anatomy, which would tell us what healthy organs look like, it is impossible to know whether what we are looking at under the microscope is normal or a sign of disease,” said Marie-Odile Benoit-Biancamano, a veterinary pathologist in the Faculty of Veterinary Medicine of Université de Montréal.

Benoit-Biancamano and her colleagues Chloé Rosa-Teijeiro and Fanny Renois decided to fill this gap by developing the first dissection protocol for the adult yellow mealworm. It was recently published in the Journal of Veterinary Diagnostic Investigation.

A container for raising mealworms
Photo : Antoine Ménard

Submerged in saline

The key innovation is that the insect is dissected while submerged in a saline solution.

After it has been euthanized and secured to a foam pad at the bottom of a tray filled with the solution, the mealworm is dissected using microsurgical instruments and a binocular dissecting microscope.

“We recreated the insect’s natural internal environment,” said Rosa-Teijeiro. “Its organs are normally bathed in hemolymph, which is its blood. Immersion keeps the tissues hydrated, improves their visibility and makes the results (of the dissection) reproducible, whereas dissection in the open air would lead to rapid drying and tearing.”

The procedure demands precision and patience: the insect is tiny, its exoskeleton rigid, and its internal organs fragile.

“Once the insect has been immobilized, we remove the elytra—the rigid wings that form the characteristic dorsal shield of beetles—and then gently lift a flap of chitin (a biopolymer) to expose the entire abdominal cavity,” said Rosa-Teijeiro.

“It’s like lifting the lid off an extremely fragile box. The organs are then isolated one by one in a specific order and documented step by step with annotated photographs.”

It took the researchers about two months, working part-time, to develop a reproducible protocol. As the method uses only standard laboratory equipment, the tools are therefore readily available, but mastering their use involves a considerable learning curve.

“It takes a few days to get used to working while looking through a binocular microscope,” noted Rosa-Teijeiro. “We usually like to see what our hands are doing.”

First complete mapping

The study provides the first complete mapping of the abdominal anatomy of both male and female mealworms, and some noteworthy observations.

In the females, the spermathecal gland—associated with the sperm storage organ—is larger than the spermatheca itself, an unusual configuration in beetles. The researchers interpret this as a reproductive advantage, as the gland provides nutrition and prolongs the viability of the stored sperm.

In the males, the testes have a flower-like shape with six follicles and two types of accessory glands that have not been documented in any other beetle species.

While they were developing the method, using mealworms from a farm, the researchers thought they were working with healthy specimens. However, subsequent histological examination—the study of tissues under a microscope—revealed granulomas and viral inclusions.

“We thought the colony was healthy, but that wasn’t exactly the case,” said Benoit-Biancamano. Parasite eggs were also found in the Malpighian tubules (the equivalent of the kidneys), in the fat body (the equivalent of the liver) and in the nervous system of some specimens.

According to Benoit-Biancamano, these serendipitous discoveries illustrate the diagnostic utility of the dissection guide. They also show that even an apparently healthy colony can harbour pathogens.

The interior of a male mealworm beetle’s abdomen, after dissection. The dark brown structures (the thin filaments) are the Malpighian tubules (the equivalent of the kidneys); the yellow structure is the digestive tract; the white area in the center of the image consists of a mixture of the male reproductive tract and the fat body (the equivalent of the liver).
Photo : Chloé Rosa-Teijeiro

A tool for breeders

For now, the method remains a research tool. The next step will be dissecting diseased insects to describe the lesions associated with known diseases. This work will transform the anatomical guide into an operational diagnostic tool for breeders.

Benoit-Biancamano’s lab now has nine students working on the insects. Other tools are being developed, including blood sampling, hemocyte count analysis, molecular diagnostics and assessing the immune response to pathogens.

Practical applications are already beginning to take shape. “We received insects from farms and were able to diagnose diseases caused by densovirus,” said Benoit-Biancamano. “So this is replicable.”

Similarly, lesions observed on dead specimens can already help identify the causative disease. This is a first step toward providing concrete veterinary support for an industry that currently has virtually none.

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