Abstarct: Tomato leaf miner, Tuta absoluta (Meyrick) (Lep: Gelechiidae) is one of the most important and key pests of tomatoes in the world, which seriously threatens the production of this product in Iran. This pest has several generations per year in favorable environmental conditions. The larvae of the pest cause significant damage to the crop by feeding on leaves, stems and fruits that in absence of control the damage will reach 100%.The role of blood cells and phenol oxidase system in the cellular defense of insects has been proven. The number of blood cells changes under the influence of any type of stress or the entry of a foreign agent into the hemolymph. To carry out the experiments of this research, the infected tomato fruits were collected from the fields of Mayamey (Gs15 cultivare) and examined after being transferred to the Faculty of Agriculture. After rearing, pest (Temprature 25±1 ◦C, humidity 50%, Light: dark, 14:10 h), larvae were used for immunological experiments. Results indicated that hemocytes included granulocytes, plasmotocytes, onocytoids, prohemocytes and spherulocytes in T. absoluta. The abundance of blood cells showed a significant increase with increasing larval age and larval weight, so that the hemolymph of fourth instar larvae showed the highest number of blood cells compared to other larval ages. The effect of different temperature stresses on the total number of cells, plasmotocytes and granulocytes as well as their morphology was quite significant, so that the total number and differentiation of cells were significantly reduced at low temperature (4±1 ◦C), and high temperature (28±1 ◦C). Morphology cell modified in thermal stresses. The cell wall of the cells became wrinkled and torn due to heat and cold and in some cases caused cell division. Also, under starvation stress in 12 and 24 hours, the total number and differentiation of cells decreased significantly. The activity of the phenol oxidase system was significantly reduced under temperature stress compared to the control and a significant decrease was also observed under temperature stress.