To investigate the host range of Spathius agrili Yang (Hymenoptera: Braconidae), a total of 18 wood boring insects either in the genus Agrilus or associated with ash forests were collected, reared, and presented to S. agrili females in no-choice tests. Results showed that S. agrili can parasitize some other insect larvae in genus of Agrilus, but attack rates were significantly lower than its natural host, emerald ash borer, Agrilus planipennisi Faimaire (Coleoptera: Buprestidae). In Y-tube olfactometer tests, female S. agrili were only attracted to twigs and leaves of EAB infested Fraxinus velutina and F. pennsylvanica, and not to 12 other potential host plants. Two other plants, Prunus persica (L.) and Ailanthus altissima (Mill.), significantly repelled the EAB. Field surveys of 17 wood boring insects, including six species of Agrilus, revealed that none of these species were parasitized by S. agrili. It was indicated that the EAB natural parasitoid S. agrili has high host specificity.
