|Cooper, William - Rodney
|RIESKE, LYNNE - University Of Kentucky
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2010
Publication Date: 6/1/2010
Citation: Cooper, W.R., Rieske, L.K. 2010. Gall structure affects ecological associations of Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae). Environ. Entomol. 39(3): 787-797.
Interpretive Summary: American chestnut was once a dominant canopy tree in Appalachian forests prior to the introduction of the fungus that causes chestnut blight. Chinese chestnut is a commercially important nut crop that is resistant to the blight. Efforts are underway to transfer blight resistance from Chinese chestnut to American chestnut for restoration purposes. The Asian chestnut gall wasp (ACGW) manipulates the growth of chestnut to produce complex growths (galls) that provide food and shelter to the young of the gall wasp. The production of galls prevents flowering and nut production, terminates shoot development, and can fatally stress trees. The ecological interactions between the ACGW, its host, and a suite of natural enemies are poorly understood. An improved understanding of ACGW ecology is critical toward the development of management programs aimed at suppressing ACGW populations in commercial or breeding orchards and American chestnut restoration programs. We collected galls from four locations in the eastern United States during a period spanning from May (gall initiation) through January (after gall wasp emergence), and evaluated the relationships between gall characteristics and attack by natural enemies. We conclude that parasitism accounted for the majority of ACGW mortality (80%), but was inhibited by certain gall characteristics including larger size and a thick woody layer surrounding gall wasp chambers. ACGW mortality was also evidenced by gall-invading fungi, empty chambers, and failure for gall wasps to emerge. Damage to the outside of galls by chestnut weevils, grazing insect herbivores, and fungal lesions may also cause ACGW mortality. This study improves our understanding of ACGW community ecology, identifies sources of mortality, and may aid in the development of biological control measures for the ACGW.
Technical Abstract: Gall wasps (Hymenoptera: Cynipidae) induce structures (galls) on their host plants which house developing wasps and provide them with protection from natural enemies. The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu, is an invasive pest that is destructive to chestnut (Castanea spp.). An improved understanding of the interactions among D. kuriphilus, its host, and its natural enemies is critical for the development of effective management strategies against this pest. The objective of our study was to evaluate the D. kuriphilus community interactions, and relate these interactions to variations among gall traits. Galls were collected from four locations throughout the eastern United States from May (gall initiation) through August (after gall wasp emergence), and January. Gall characteristics (volume, weight, and schlerenchyma layer thickness), gall inhabitants (D. kuriphilus, parasitoids, and chamber fungi), and other community associates (insect herbivores and lesions thought to be caused by endophytes) were evaluated and correlated using canonical correlation analyses. The primary mortality factors for D. kuriphilus were parasitism, gall chamber-invading fungi, and failure of adult gall wasps to emerge. Larger gall size and thicker schlerenchyma layers surrounding the larval chambers were negatively correlated with parasitoids and chamber fungi, indicating these gall traits are important defenses. External fungal lesions and insect herbivory were positively correlated with the absence of D. kuriphilus within galls. This study provides support for the protective role of cynipid galls for the gall inducer, identifies specific gall traits which influence gall wasp mortality, and improves our knowledge of D. kuriphilus ecology in North America.