Histological Atlas of the Internal Anatomy of Female Varroa destructor (Mesostigmata: Varroidae) Mites in Relation to Feeding and Reproduction

Abstract

Abstract Histochemical staining of histological sections of Varroa destructor (Anderson andTrueman, 2000) mites reveal the internal body plan and are used to contrast the internal organs associated with feeding and reproduction of starved versus recently fed female mites.The gnathosoma is comprised of a powerful sucking pharynx, which employs 11 alternating dilator and constrictor muscles, the chelicerae, the salivary ducts, and the salivarium. Coronally, the esophagus is visible through the synganglion between its supraesophageal and subesophageal regions and connects posteriorly to the midgut.The midgut is devoid of food particles in starved mites, but in fed mites, the midgut epithelial cells are filled with innumerable globular spheroids replete with lipoproteins, including polyunsaturated lipids, whereas the lumen is filled with saturated lipids or other unidentified nutrients. In the opisthosomal body region of the fed female, the bilobed lyrate organ lies adjacent to the midgut on one side and the ovary on the opposite side, with very close cell to cell linkages that appear to form a syncytium. The fed female ovary contains an enormously enlarged ovum, and numerous elongated nurse cells extending from the lyrate organ. Dyes staining selectively for lipoproteins suggests rapid incorporation of neutral and polyunsaturated lipids and lipoproteins. Also evident near the ovary in fed females is the spermatheca filled with elongated, fully capacitated spermatozoa. The histological and histochemical findings reported in this study provide a fresh insight into the body structure, nutrition, and reproductive activity of the female of this harmful honey bee parasite and disease vector. Graphical Abstract Representative images histological atlas varroa destructor (Mesostimate:Varroidae): A. Anterior body region showing the pharynx, esophagus, sunganglion and salivary gland (sagittal view); B. Mid-section of body showing intracellularvesicles (lipoproteins) in epithelial cells of the midgut (sagittal view). C. Posterior region of body showing of the ovary with developing oocytes connected by elongated nurse cells to the lyrate organ: D. Posterior region of body showing the ovary with a very large developing oocyte, adjacent spermatheca and lyrate organ. All images are fed females.