Two states of parasitization in the Pseudaletia separata-Cotesia kariyai system were examined: one that was lightly parasitized and one that was heavily parasitized. We predicted that the consumption of fat body and hemolymph nutrients depends on the number of parasitoid larvae in the host. Lightly parasitized hosts (average clutch size[plus or minus]S.E.: 42.5[plus or minus]16.2, N=15) and heavily parasitized hosts (average clutch size[plus or minus]S.E.: 230.2[plus or minus]8.8, N=15) were prepared artificially. Eight days after parasitization, perivisceral fat body was depleted in the heavily parasitized host, although peripheral fat body was not yet consumed, but by day 10 most of the peripheral fat body was consumed. In lightly parasitized hosts, perivisceral fat body was not consumed by day 10. The parasitoid larvae deplete the perivisceral fat body first and then consume the peripheral fat body in the heavily parasitized host. The amount of trehalose, the major carbohydrate in the hemolymph, was related to the number of parasitoid larvae developing in the host. In a heavily parasitized host, trehalose concentrations remained low. However, in lightly parasitized hosts, the amount of trehalose increased 8 days after parasitization and then decreased by day 10. Protein and total lipid concentrations in the hemolymph of the heavily parasitized host were significantly lower than in lightly parasitized host on day 10, suggesting that the large number of parasitoid larvae depleted the fat body and hemolymph nutrients by day 10. High concentrations of total lipid on day 8 and 10 in lightly parasitized hosts and on day 8 in heavily parasitized host are likely to be attributed to the teratocytes. General morphology; Biochemistry; Circulatory system; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Pseudaletia separata (Noctuidae); Fat body; Biochemistry; Chemical composition; Haemolymph; Hymenopteran parasites; Cotesia kariyai; Prevalence, haemolymph composition & fat body consumption by parasites relations Cotesia kariyai (Braconidae); Lepidopteran hosts; Pseudaletia separata; Prevalence, host haemolymph composition & fat body consumption relations none