We compared the production of pseudoparasitization by Microplitis rufiventris females in most (third) and less (fourth) preferred instars of Spodoptera littoralis larvae at 20 [plus or minus] 1 and 27 [plus or minus] 1 [degree]C. The parasitized hosts were classified into hosts producing parasitoids (type A hosts) and hosts producing no parasitoids, i.e., pseudoparasitized hosts (type B hosts). The latter were further classified into: (a) pseudoparasitized hosts with "well" arrested development (type B1 hosts); (b) pseudoparasitized hosts with partially arrested development (type B2 hosts); and (c) pseudoparasitized hosts that successfully pupated to apparently normal host pupae (type B3 hosts). The present series of experiments showed that parasitization by M. rufiventris was clearly affected by host instar, age within an instar and rearing temperature. Production of type B hosts was less when third instar S. littoralis larvae were exposed to the wasp females than when the host larvae were in fourth instar. The production of type A hosts was much greater when early or mid ages of an instar was stung by the wasp females comparing with stung late age of the same instar. Production of type B hosts may be due to one or overall of the following: (a) dosage dilution of M. rufiventris female's factors in the different age classes of the instar; (b) endocrine system (physiological state) at parasitization time, i.e., early vs late age of the instar; (c) growth rate of host larvae. The lowest production of type B hosts was at highest growth rate; and (d) temperature, larger proportions of type B hosts were produced at 27 [plus or minus] 1 [degree]C than at 20 [plus or minus] 1 [degree]C. Biometrics; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Physical factors Spodoptera littoralis (Noctuidae); Age; Hymenopteran parasites; Microplitis rufiventris; Pseudoparasitism occurrence, host instar, age & temperature relationships; Temperature Microplitis rufiventris (Braconidae); Lepidopteran hosts; Spodoptera littoralis; Pseudoparasitization, effects of host instar, age & temperature; Temperature none