Abstarct: Fig (Ficus carica L.) is a perennial tree of the Moraceae family. Phycodes radiata is a leaf-eating and monophagous pest of figs, which has been damaging in Semnan fig orchards in recent years. In this research, the biology of P. radiata in laboratory conditions on four varieties of figs (yellow, red, garmsar, foresty), feeding index and immune reaction of larvae against Beauveria bassiana was studied. Insect egg clusters were collected from fig trees in spring and transported to the laboratory. The larvae were fed daily by fig leaves of the corresponding variety. The length of the body and the width of the head capsule were the criteria to distinguish different larval ages. Body length and body width with open wings were recorded in insects. Determining the sex of male and female by the black band on the front wings and the size and color of the antennae. The period of growth and development by feeding different cultivars had a significant difference in each growth stage. The length of the larval and pupal period in the fed larvae was longer in foresty fig variety and shorter in yellow variety than other varieties. The lifespan of male and female that had fed on foresty figs during their larval stage was longer than that of other larvae. The larvae of this insect feed on the leaves, fruits, and buds of different varieties of figs in the garden and in the laboratory, and during feeding, they secrete silk threads and leave their black and dry excrement inside the threads and leaves of figs. Feed index as a statistical index to evaluate the performance of larvae on four varieties of figs showed that the larvae showed the best feeding and digestion process on Semnan yellow variety and the weakest performance on forest figs. In immunology section, the results showed that four types of hemocytes including prohemocytes, plasmatocytes, granulocytes, and onocytoids are present in the hemolymph of the larvae of P. rediata, which can be identified after staining with Giemsa's color solution and by light microscopy. The abundance of blood cells in the 5th instar larvae was also investigated. The results showed that along with the increase in larval age, the number of hemocytes increased significantly. So, the density of granulocytes and plasmotocytes was the highest in 4th and 5th instar larvae. The immune response of 5th instar larvae against 5 isolates of B. bassiana including isolates N1, N4, b2, f4 and 47 was positive. A concentration of 105 spores/ml of fungal isolates was injected into the larvae and the activity of hemocytes was evaluated after 1, 3, 6, 12, 24, 48 and 72 h. Control larvae included larvae that were injected with distilled water and 80% tween. The total number of cells and the number of plasmatocytes and granulocytes were significantly higher than other treatments at 3 and 6 hours after the injection of isolates b2 and 47. The results of this study showed that P. radiata larvae had a acceptable defensive activity against the spores of these isolates