Morphological characterization and percentage of circulating haemocytes of European hornet Vespa crabro L. (Hymenoptera: Vespidae)

This study represents the first data for size, morphology, surface area and a number of haemocytes in European hornet ( Vespa crabro ). Circulating haemocytes were microscopically characterized and their surface was determined by software for image analysis. Three types of haemocytes have been identified: granulocytes, basophilic haemocytes and plasmatocytes. Granulocytes are the dominant type of haemocytes with smallest surface area (54.10±2.42; A =25.79 μm 2 ), plasmatocytes are the largest circulating haematocytes (41.70±2.41; A= 123.56 μm 2 ), and basophilic haemocytes are the least represented (4.20±1.03; A= 49.35 μm 2 ). In addition to circulating haemocytes, we recorded two types of “giant” haematocyte, representing the first data in insects. These cells undergo various transformation stages and mature into large cells. The morphology of these haemocytes and the developmental stages indicate that they may originate from plasmatocytes and basophilic haemocytes. “Giant cell type I” probably originates from plasmatocyte and has a surface area A= 3664.62 μm2. „Giant cell type II“  is formed by the transformation of basophilic haematocyte and has surface area A= 8411.66 μm 2 . Phagocytosis was found in giant cells type II. The developmental stages of giant haematocytes are presumably result of physiological processes related to phagocytosis and their role in immunity. Future studies should provide more information about types, developmental stages of haemocytes including larval hemocytes and phagocytosis which will contribute to the understanding of many physiological and immune processes in these insects.