none Ostrinia nubilalis; HYMENOPTERAN-PARASITES; Macrocentrus grandii; Host location, role of olfactory response to host food plants Macrocentrus grandii; CHEMORECEPTION-; TAXIS-; Olfactory response to lepidopteran host food plants, role in host location; LEPIDOPTERAN-HOSTS; Ostrinia nubilalis; Host location, role of olfactory response to host food plants. In an earlier study we documented attraction of the specialist parasitoid Macrocentrus grandii Goidanich to odors of corn, potato, and snap bean. In the present study the chemical bases of the parasitoid's attraction to these food plants of its European corn borer host were compared. Volatile compounds from corn leaves were isolated using Tenax and identified by capillary gas chromatographic-mass spectrometry. Twenty-one compounds including aldehydes, ketones, alcohols, esters, and sesquiterpenes were present in corn. These were separated into fractions by column chromatrography on Florisil. Wind-tunnel bioassays of the fractions indicated that M. grandii was attracted to fractions containing nonpolar and slightly polar compounds including sesquiterpenes, aldehydes, a ketone, and esters. More polar compounds in corn, like alcohols, were not attractive. Attraction to potato odor was based on the presence of the same classes of compounds that were atractive in corn, but more polar compounds were involved in attraction to snap bean odor. This study indicated that only some compounds in each of the three odor complxes tested were attractive. It also documented that different compounds were involved in attraction of M. grandii to different plant odors.