THE ULTRASTRUCTURE OF HEMOCYTES IN DACTYLOPIUS-CONFUSUS (COCKERELL), AND THE ROLE OF GRANULOCYTES IN THE SYNTHESIS OF COCHINEAL DYE

The ultrastructural study of free circulating hemocytes in the adult c ochineal scale, Dactylopius confusus (Cockerell), demonstrated five ce ll types: prohemocytes, typical granulocytes (T-granulocytes), oenocyt oids, plasmatocytes, and granulocytes with modified sub-cellular struc ture to perform a special synthetic and secretory function, which we r efer to as ''modified granulocytes'' (M-granulocytes). Prohemocytes sh owed undifferentiated sub-cellular structure of the basic stem cell ty pe (i.e., high cytoplasmic density with numerous ribosomes, centrally located large nucleus with a distinct nucleolus, and poorly developed endoplasmic reticulum). The commonly observed typical granulocytes (T- granulocytes) had several smooth endoplasmic reticulum (SER) with dila ted cisternae and many SER-derived membrane bounded granules of differ ent sizes and electron density. Oenocytoids were identified by the pre sence of many crystals, RER-originated fine secretory granules, and an eccentric nucleus. Plasmatocytes were easily characterized by their v ariable shapes and irregular outline with pseudopodia-like cytoplasmic extensions, possession of an elongated lobed nucleus, multivesicular bodies, RER-derived membrane bounded, electron-dense, lysosome like va cuoles, well-developed SER cisternae, and numerous pinocytic and SER-o riginated vesicles of different sizes along the peripheral region. M-g ranulocytes comprised the largest proportion of hemocytes in all sampl es observed. M-granulocytes were distinguished not only by the presenc e of membrane bounded granules of different sizes and electron density , but by the possession of large nuclei with distinct nucleoli, many m itochondria, and a highly developed network of rough endoplasmic retic ulum (RER). M-granulocytes had abundant, rosette-shaped, RER-derived c hains of fine secretory granules, which accumulated in the cytoplasm a nd vacuoles, and were ultimately deposited into the hemolymph by exocy tosis. These fine granules gave a positive result with periodic acid-S chiff (PAS) test. Based on RER-synthesized fine secretory granules (M- granulocytes), their ultimate deposition into hemolymph, the red pigme ntation of hemolymph, positive PAS histochemical test of these granule s, and the high population of these hemocytes, no such cell type has b een described in previous studies in insects. The sub-cellular structu re of the granulocyte in this insect has been modified to perform a sp ecial synthetic and secretory function (i.e., possibly the synthesis o f the red pigment found in hemolymph, which has been the source of com mercially important cochineal dye).