STUDIES ON THE LARVAL HEMOCYTES IN THE CABBAGE WHITE BUTTERFLY, PIERIS RAPAE CRUCIVORA BOISDUVAL, WITH SPECIAL REFERENCE TO HEMOCYTE CLASSIFICATION, PHAGOCYTIC ACTIVITY AND ENCAPSULATIVE CAPACITY

The present investigation was undertaken to identify the cell types of hemocytes concerned with phagocytosis and encapsulation of foreign particles (India ink or acrylonitrile-styrene particles) injected into the body cavity of the fifth-instar larva of Pieris rapae crucivora. 1. The hemocytes were observed and classified in unfixed (=living) or heat-fixed samples with an ordinary or a phase contrast microscope at 400 to 1000X and also in supravital (neutral red), Giemsa's, and hematoxylin-erythrosine B stained smears. According to the morphological characteristics of the hemocytes, the following categories of circulating hemocytes can be identified : (a) prohemocytes ; (b) plasmatocytes ; (c) granular hemocytes ; and (d) oenocytoids. This classification and terminology are compared with those of Iwasaki (1930). It is suggested that both of the hemocytes which Iwasaki termed phagocyte and spherule cell are comparable to the granular hemocyte, and the plasmatocyte is one type of the hemocytes which he called proleucocyte. 2. Each larva had an injection of 0.0456g of India ink containing 118560±9700 carbon-particles per mm^3, and phagocytic capacities, total hemocyte counts (THCs) and differential hemocyte counts (DHCs) in the larvae injected were examined by three drops of heat-fixed hemolymph obtained from the severed first abdominal legs at the following intervals after injection : 2, 4, 6, 24, 48 and 72 hours. 3. The percentage of phagocytosis was greatest at 48hr after injection and the most active hemocyte involved in phagocytosis was granular hemocyte. 4. Granular hemocytes showed a trend to increase and plasmatocytes to decrease in number with time from 2hr after injection. 5. Total hemocyte counts showed a decrease with time from 4hr after injection, there were, however, a possible trend to recover to the normal level at 72hr after injection. 6. The identification of the cell type concerned with encapsulation of foreign pa rticles were made by the following method : Two or three particles, 30 to 40μ in diameter, of acrylonitrile-styrene were injected into the hemocoele with saline for Bombyx by inserting a Salt's micropipette into the ventral surface of Pieris larvae between the first and second abdominal legs. Two days after injection, the larvae injected were dissected in saline under a binocular microscope and the hemocytes encapsulating the particles were examined under a phase contrast microscope. Plasmatocytes were the principal hemocytes involved in encapsulation of the particles, but it seemed that granular hemocytes were also concerned.