Hemogram study and effect of thermal Stresses on abundance of immunocytes in larvae of Goat Moth, Cossus cossus (Lepidoptera: Cossidae)

The introduction of pathogens, infections and environmental pollutants into the insect hemolymphs, thermal stresses and nutritional diet changes, affect the insect immune system. Insect immunity consists of components that hemocytes are the main components of them. In the present study, the morphology and changes in density of hemocytes in the hemolymph of the Cossus cossus L. were studied against thermal stresses. The hemocytes of all larval stages of C. cossus were examined by Giemsa and the response of these cells was evaluated at temperatures of 4 °C and 30 °C. Five identified types of hemocyte in this insect were; Prohemocyte, Plasmatocyte, Granulocyte, Oenocytoide and Spherulocyte. All hemocytes types were detected in each stage but frequency of them in each stage was different. Total Hemocyte Count showed that by increasing larval instars and body size, hemocyte rate increased gradually. Differential count hemocyte indicated that plasmatocytes and granulocytes are the most abundance in 5th and 6th instars larvae. So 5th and 6th instars larvae have the highest blood volum and hemocyte count. Granulocytes showed the highest abundance variation in heat and chill stress, and plasmatocytes also decreased significantly under the influence of chill stress. It seems that recognizing the hemocyte characteristics of this pest and the frequency of immunocyte changes against to thermal stresses, can be considered as an introduction on immunological studies of this pest. Surely, further investigation is needed to investigate the interaction of the immune system of C. cossus with pathogens and to evaluate the efficacy of microbiological control.