A native and an introduced parasitoid utilize an exotic gall-maker host

Authors: Cooper, William - Rodney; RIESKE, LYNNE - University Of Kentucky

Submitted to: BioControl
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2011
Publication Date: 9/16/2011
Citation: Cooper, W.R., Rieske, L.K. 2011. A native and an introduced parasitoid utilize an exotic gall-maker host. Biocontrol. 56(5):725-734.

Interpretive Summary: The Asian chestnut gall wasp is an invasive pest of chestnut trees that threatens commercial chestnut production and efforts to restore American chestnut to Appalachian forests. This pest is attacked by at least two parasitic wasps (parasitoids), one that is native to the U.S. (Ormyrus labotus) and that has been introduced from the native range of the gall wasp (Torymus sinensis). Key to the development of management plans to control the Asian chestnut gall wasp is an understanding of the interactions between this pest and its native and introduced natural enemies. We studied these interactions in orchard, forest, and suburban settings. The introduced parasitoid, T. sinensis, was collected from all study sites on all dates of collection, and was the dominant parasitoid in orchard and suburban settings. The native parasitoid, O. labotus, was more prevalent in the forest setting, and was only observed on a portion of the collection dates. The absence of O. labotus on some collection dates suggests it also attacks native gall wasps, which are most available in the forest setting. Observations suggested that the native parasitoid may also attack the introduced parasitoid. In this case, establishment of the introduced parasitoid may be inhibited in forest locations were O. labotus is abundant. Our study suggests that habitat influences parasitism of the Asian chestnut gall wasp by the introduced and native parasitoids. These results may facilitate implementation of biological controls against this gall wasp in commercial orchards and Appalachian forests.

Technical Abstract: Dryocosmus kuriphilus (Hymenoptera: Cynipidae) is non-native to North America and induces formation of galls on petioles and leaves of all chestnut (Castanea spp., Fagales: Fagaceae). We investigated the interactions between the gall wasp D. kuriphilus, a native parasitoid, Ormyrus labotus (Hymenoptera: Ormyridae), and a non-native parasitoid, Torymus sinensis (Hymenoptera: Torymidae). Galls were collected monthly from May to August and in January from four locations in the United States consisting of orchard-grown hybrid chestnuts (Hiram, OH and Meadowview, VA), suburban-grown ornamental Chinese chestnuts (C. mollissima) (Broadview Heights, OH), or forest-grown American chestnuts (C. dentata) (Bowling Green, KY). Parasitoids were removed from galls and T. sinensis and O. labotus were identified using PCR-markers. The relative abundance of each parasitoid was compared in relation to collection date, habitat, presence of alternative hosts, and gall characteristics. T. sinensis was collected from each location and date, and was dominant in the orchards and suburban locations. However, relatively more O. labotus were collected within the forest, which had significant oak component and alternative cynipid hosts. O. labotus was only collected in spring and early summer, indicating the use of different summer and winter hosts. Observations suggest that in addition to parasitizing D. kuriphilus, O. labotus hyperparasitizes T. sinensis. T. sinensis has a longer ovipositor than O. labotus, and parasitized larger galls. This study improves our understanding of interactions between an invasive gall wasp, an introduced parasitoid, and native parasitoids, and illustrates novel relationships that may form as exotic species expand their geographic range.