none The olfactory responses of Macrocentrus grandii Goidanich, a larval parasitoid of the polyphagous European corn borer (ECB), Ostrinia nubilalis (Huebner) to 51 species of plants were assayed in a laboratory olfactometer. Naive female parasitoids exhibited positive responses to 15 species and negative responses to 7 species. There was no correlation of parasitoid response with a plant's status as an ECB host or non-host. Attraction was strongest to corn, Zea mays L. Experienced females preferred the species (corn, potato or sunflower) on which they previously had found host ECB, even when the plant (sunflower) was not attractive to naive females. The response of experienced females to the odor of sunflower stem declined significantly after the third day post-experience.