The relationship between temperature and development ofUraba lugensWalker and between temperature, host size, and development of its parasitoids,Cotesia urabaeAustin and Allen andDolichogenidea eucalyptiAustin and Allen, were investigated.U. lugensunderwent from 6 to 14 instars before pupation. The number of instars affected the allometry of head capsules. Females had more instars than males, and both sexes had more instars at lower temperatures. Thermal requirements for larval and pupal development ofU. lugensdiffered between sexes; male larvae had lower temperature thresholds and male pupae higher temperature thresholds than females. Egg–larval rate of development ofC. urabaeafter oviposition in small hosts was much slower than that after oviposition in midsize hosts and differed between sexes. Pupal development ofC. urabaewas faster for males than females. Egg–larval development ofD. eucalyptiafter oviposition in small hosts was more rapid than that ofC. urabaefrom small hosts, whereas pupal development ofD. eucalyptiwas slightly longer than that ofC. urabae. WhenD. eucalyptiwere reared at 15°C, some individuals pupated when predicted by degree-day summation, and others delayed emergence from the host by a further 120–182 d, indicating a physiological delay in development. Simulation of the phenologies ofU. lugens, C. urabae, andD. eucalyptiin the Adelaide region using thermal constants showed good fit between field-observed and predicted durations of life stages and confirmed the presence of a physiological delay in emergence ofD. eucalyptiin winter and during its second generation in summer.