The morphology of the female reproductive system of pupal and adult stages of Microplitis rufiventris and the ultrastructure of the ovaries are described and illustrated. Two morphologically distinct types of particles of nuclear origin, i.e., polydnavirus (PDV) and a virus-like filamentous particle (VLFP) were detected in the ovarian calyx fluid of the female wasp. It is likely that these particles are injected into the host during oviposition. PDV initiated replication in the calyx of mid-aged pupae and in pharate adults and were present throughout adult life. VLFP were only seen in the calyx fluid of newly emerged adults, and therefore observed after the PDV. Feulgen and methyl-green pyronin staining revealed the presence of DNA in both types of particles. The effects of injection of Spodoptera littoralis larvae with a combination of parasitoid viruses and venom of M. rufiventris females (CxFV) were investigated and the results were compared with two control groups, i.e., larvae injected with Pringle's saline (PS) and naturally parasitized larvae. CxFV-larvae showed significant declines (P0.05) in food consumption, weight of ejected faeces and weight gain when compared with PS-larvae. However, naturally parasitized larvae (parasitoid egg+CxFV+ovarian protein) displayed a high significance score (P0.01) in comparison with those of PS-larvae. The approximate digestibility (AD) values of S. littoralis larvae were positively affected as early as day 2 post-treatment by either injection of CxFV or parasitization. However, a reduction in AD was observed in both PS- and CxFV-larvae on day 3-7 in comparison with naturally parasitized larvae. Other indices of food utilization were unchanged in CxFV-larvae when compared to saline treated or parasitized controls. [copyright] 2005 Elsevier Ltd. All rights reserved. Spodoptera littoralis (Noctuidae) : Host Microplitis rufiventris (Braconidae) : Parasite Biometrics; Nutrition; Energy budget; Reproduction; Reproductive system; Gonad; Life cycle and development; Development; Growth; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Microplitis rufiventris; Reproductive system; Ovary; Ducts of female; Calyx; Lepidopteran hosts; Host growth & energetics; effects of virus-like particles from parasite calyx fluid; Spodoptera littoralis Spodoptera littoralis; Weight; Energy intake; Food conversion efficiency; Feeding rate; Larval development; Growth rate; Hymenopteran parasites; Host growth & energetics; effects of virus-like particles from parasite calyx fluid; Microplitis rufiventris none