Life-Stage-Specific Hematological Profiles in Yellow Mealworm Beetles (Tenebrio molitor): Reference Intervals and Hemocyte Characterization.

BACKGROUND

The edible insect industry, driven by the nutritional and environmental benefits of mealworms, faces increasing challenges from pathogens affecting Tenebrio molitor farming systems. Hemocyte-based health assessments could provide valuable diagnostic insights, yet standardized hemolymph processing protocols and hematological reference intervals (RIs) are currently lacking for this species.

OBJECTIVES

This study aimed to develop practical protocols for hemolymph sampling, refine hemocyte classification, and establish hematological RIs for both larval and adult stages of T. molitor.

METHODS

An optimized tearing method, involving capillary collection of hemolymph from a proleg transected at the femoral-tibial joint, was used to sample healthy individuals. Total and differential hemocyte counts were determined using a hemocytometer and Wright-Giemsa-stained smears, respectively, and from distinct insect populations (n = 41-43 samples per group). Hemolymph was analyzed in pools due to the small size of T. molitor. Transmission electron microscopy was conducted on a multinucleated giant hemocyte (MGH) isolated from a histologic slide. RIs were calculated following American Society for Veterinary Clinical Pathology (ASVCP) guidelines, and life-stage differences were statistically assessed.

RESULTS

Granular cells and plasmatocytes predominated, whereas prohemocytes and oenocytoids were rare. MGHs, newly identified in T. molitor, were characterized as a fifth hemocyte population. Significant life-stage differences were observed, warranting separate RIs for larvae and adults. The established RIs were relatively wide, reflecting natural fluctuations in invertebrate hemolymph volume and the unsexed, age-diverse reference population.

CONCLUSIONS

This report of hematological RIs for T. molitor lays the groundwork for implementing hemocyte-based health surveillance in yellow mealworm beetle farming.