MORPHOLOGICAL AND CYTOSKELETAL CHARACTERIZATION OF HEMOCYTES IN STICKINSECTS (PHASMATODEA)

The cell content of the hemolymph from the two species of stick insect s Bacillus rossius and Carausius morosus was characterized in morpholo gy and cytoskeletal distribution by flow cytometric analysis, phase-co ntrast microscopy, and scanning electron microscopy. In in vitro cultu red hemocytes, the cytoplasmic distribution of F-actin microfilaments was revealed with Rhodamine-labelled phalloidin, and that of microtubu les by indirect immunofluorescence with a monoclonal anti a-tubulin. T he results show that both stick insects possess peculiar hemocyte subp opulations, as detected by flow cytometry, composed of plasmatocytic a nd granulocytic cells. Carausius morosus has a hemocyte subtype, the s pherulocyte, that appears to be lacking in Bacillus rossius. The resul ts of cytoskeletal analysis show that the plasmatocytes of both specie s, smeared on glass coverslips and compared with cultured mammalian ep ithelial control cells, possess a regular cytoskeletal network, with F -actin microfilaments organized in stress-fibres, and microtubules spa nning the cytoplasm. In rounded, non-plasmatocytic cells, the F-actin stress-fibres were not detected, and the microtubules were arranged in a fashion resembling that present in human lymphocytes. These data ma y reflect different functional and/or immunological specializations am ong stick insect hemocyte subpopulations, and suggest similarities in cytoskeletal organization and cell isotypes between insect and vertebr ate blood cells.