Abstract Eggs ofthe eucalyptus longhorned borer ( Phoracantha semipunctata F.) are the typical host of the encyrtid egg parasitoid Avetianella longoi Siscaro. Both P. semipunctata and Phoracantha recurva Newman have become established in California, but A. longoi appears to differentially parasitize these congeners. Eggs of the two beetle species were tested for ovipositional and developmental suitability for A. longoi at 0.5, 1.5, 2.5, 3.5, and 4.5 days after deposition in both no-choice and choice bioassays. In no-choice experiments, the parasitoid oviposition rate was similar in the two host species when the host eggs were 0.5 days old, but higher in P. semipunctata eggs when the host eggs were ≥1.5 days old. Females allocated significantly more eggs per host egg to P. semipunctata eggs than to P. recurva eggs when the eggs were 0.5–3.5 days old. Survival of the parasitoids was significantly lower in P. recurva eggs of all age classes than in P. semipunctata eggs. In choice experiments, female parasitoid oviposition rate was significantly higher in P. semipunctata eggs regardless of host egg age. Parasitoid survival was also significantly higher in P. semipunctata eggs. In both choice and no-choice experiments, some P. recurva embryos survived the parasitoid attack and emerged as neonate larvae from parasitized eggs, whereas P. semipunctata embryos never successfully developed in parasitized eggs. These results have important implications for biological control of the two beetle species by A. longoi.