Study on morphology and frequency of hemocytes in Osphranteria coerulescense (Redt) (Coleoptera: Cerambycidae) and Zeuzera pyrina L. (Lepidoptera: Cossidae) larvae, two wood boring insects of Iran

Hemocytes as the immune system are important factors against fungi, bacteria and insecticide particles. Studying the morphology of hemocytes and their frequency is essential as the first stage in identification of cellular immune characteristics. In the present research, the types of hemocytes were investigated in the haemolymph of Osphranteria coerulescense and Zeuzera pyrina larvae after staining with Giemsa and by light microscopy at 40x magnification. Four types of hemocytes including prohemocytes, plasmotocytes, granulocytes and oenocytoides were identified in hemolymph of both pests. Spherulocytes and podocytes were observed only in hemolymph of Z. pyrina and 2nd and 3rd instars larvae of Osphranteria coerulescense, respectively. Prohemocytes as stem cells were small and often round with central nucleus. Plasmotocytes had often polymorphism profile and together with granulocytes were the most abundant hemocytes in both insects. Granulocytes are variable in size, round or oval shape with large nucleus in relation to cell size. They were the most abundant cells in the hemolymph of 4th and 5th instars of Zeuzera pyrina. Oenocytoid were also found to be generally small to medium-sized, oval shape with round and eccentrical nucleus. Spherulocytes were usually rounded or elongated cells and larger than Granulocytes. The total hemocytes count at different larval stages of both insects showed that the number of cells was directly related to larval age. The total number of cells was higher in the 3rd instar larvae of O. coerulescence and 5th instar larvae of Z. pyrina in comparison to the other instars. Differential hemocyte count showed that frequency of Plasmotocytes and Granulocytes were the highest in all of larval instars. The present study provides detailed information of hemocyte profile and hemogram of two wood boring insects. These findings could be used as a basis for further investigation on the immunology studies of Osphranteria coerulescense and Zeuzera pyrina.