The eucalyptus longhorned borer, Phoracantha semipunctata (F.) (Coleoptera: Cerambycidae), is under complete biological control in California following introduction of the encyrtid egg parasitoid, Avetianella longoi Siscaro. The cerambycid congener, Phoracantha recurva Newman¸ subsequently established in the state and has been subject to limited parasitization by the wasp. Behavioral analysis demonstrated that female parasitoids follow the same sequence of ovipositional behaviors when encountering eggs of both beetle species, but discriminate between the species and make a decision to lay an egg only after inserting the ovipositor into an egg. Previous research has demonstrated that the eggs of P. recurva are capable of encapsulating and killing eggs of A. longoi. Eggs of P. semipunctata do not produce a host defense to parasitization. Consequently, the ability of a female to distinguish between the congeneric species has critical fitness consequences.