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Hemocyte Comparison in Stick Insect and Cockroaches

The aim of this study was to characterize and quantify hemocyte types in Indian stick insect (Carausius morosus), American cockroach (Periplaneta americana), Deathshead cockroach (Bleberus craniifer) and Cave cockroach (Archimandrita tessellata). Total (THC) and differential (DHC) hemocyte counts were performed and the results were compared. Insects are by far the largest and the most heterogeneous group of organisms on Earth that dominate land found in freshwater and sea as well. It is estimated that there are at least 800 000 species of insects on Earth today. Although insects have been studied for years, their circulatory system has remained unexplored to great extent. The insect body fluid, hemolymph, circulates freely around the internal organs (2). It consists of hemocytes and the fluid. Hemocytes, insect blood cells, play an important role in the insect immune system (3). Wider knowledge on hemocytes would contribute to a better understanding of the insect immune system (1). Insects were kept on room temperature (24°C) and fed with ivy leaves. They were sprinkled with water once a day. To collect hemolymph, insects were put in hot water (60°C) for two minutes, to prevent blood coagulation. Hemolymph was transferred on a glass coverslip with a micropipette. Hemocytes were fixed in methanol for 15 minutes and dyed with Giemsa stain (G) for three minutes. THC was performed by standard procedure in Bürker-Türk chambers on five individuals of each species. For DHC a hundred hemocyte cells per individual were analyzed, five individuals per species. Both THC and DHC were made by using Olympus CX41 light microscope. Preparations were photographed by using Olympus E-1 digital camera and "QuickPhotoPRO 2.0" computer program. THC in species B. craniifer varied between 63-90 000 hemocytes/&micro ; L of hemolymph, while DHC showed that there were present five types of hemocytes: plasmatocytes (34-52 %), spherulocytes (35-44 %), prohemocytes (1-3 %), granulocytes (7-15 %), coagulocytes (1-6 %). THC in species P. americana varied between 70-120 000 hemocytes/&micro ; L of hemolymph. DHC in this species showed three types of hemocytes: plasmatocytes (86-91 %), prohemocytes (6-11 %), coagulocytes (3-5 %). THC in A. tessellata varied between 33-60 000 blood cells/&micro ; L of hemolymph. DHC showed five types of blood cells: spherulocytes (45-56 %), plasmatocytes (17-29 %), granulocytes (10-15 %), prohemocytes (3-8 %), coagulocytes (3-8 %). In C. morosus THC varied between 11-17 000 hemocytes/&micro ; L of blood. DHC showed 4 types of cells: plasmatocytes (66-76 %), prohemocytes (10-18 %), granulocytes (8-12 %) and coagulocytes (4-9 %). Although the three out of four species of studied insects belong to the same order (Dyctioptera), two of which belong to the same suborder (Blaberidae), the differences in THC between the species were extremely high. The lowest THC of all studied species has C. morosus. Although B. craniifer and A. tessellata belong to the same suborder, their THC was not alike. The biggest differences were visible between P. americana and other cockroaches. We suppose that those differences occurred because P. americana is not a tropical species as the other, and their habitats differ. DHC varied from species to species. Tropical species of cockroaches (B. craniifer, A. tessellata) had the most similar DHC. They had the highest concentration of spherulocytes, which were not found in other species. All the species contained prohemocytes, plasmatocytes and coagulocytes. P. americana did not contain granulocytes and spherulocytes, while C. morosus did not contain spherulocytes. Plasmatocytes and spherulocytes were highly concentrated in the hemolymph. All the species had a relatively low concentration of coagulocytes in their blood. Wider knowledge of insect THC and DHC could be the key to understanding their defense system, since hemocytes play an important role in phagocytosis and blood coagulation.

hemocytes; cockroaches; stick insect

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