The egg parasitoid, Avetianella longoi, attacks Eucalyptus long-horned beetles (F. Cerambycidae: Genus Phoracantha). This wasp preferentially attacks P. semipunctata rather than a congener, P. recurva. Furthermore, wasp development in the latter species and is much less successful. This reduced success was found to be partially due to encapsulation of the developing wasp by the host egg. Encapsulation rates were highly variable and parasitoid success was related to host age at parasitization and to superparasitism rates. Unlike P. semipunctata, which is highly susceptible to parasitism, a substantial percentage of parasitized P. recurva eggs survived parasitization and produced viable beetle larvae. Beetle resistance to the parasitoid was found to have a strong negative correlation with superparasitism (R2=0.919). Thus, parasitoid progeny were more likely to survive in superparasitized host eggs, and the data suggested a “dose response” type effect. Isofemale lines of either beetles or wasps were used to determine if resistance, avoidance of encapsulation, and superparasitism were predictable traits.