Research Accomplishment Reports 2007

Herbivory in Deciduous Forests: Implications for Forest Regeneration and Restoration

L.K. Rieske-Kinney
Department of Entomology

 

Project Description

We are investigating ecological interactions associated with an exotic invasive species, the Asian chestnut gall wasp. Molecular techniques are being used for parasitoid identification, for detailed examination of the effects of natural enemies in regulating gall wasp populations, with the goal of managing expanding gall wasp populations. The role of jasmonic acid, a plant signaling compound, in the defense response of chestnut is being studied. Jasmonic acid induces the production of defensive tannins in a species- and tissue-specific manner. JA applied to American chestnut reduces suitability for Asian chestnut gall wasp, but does not affect adjacent foliage. JA applied to Chinese chestnut enhances suitability for the gall wasp, and increases the defensive response in adjacent foliage, affecting subsequent herbivores. This improves our understanding of tree defenses and the role of tannins, and helps elucidate ecologically important differences in tannin induction and herbivore susceptibility in Castanea.

Long term monitoring plots to assess the ecological effects of the hemlock woolly adelgid, an exotic invasive herbivore that kills hemlocks, have been established. We are assessing vegetative composition and structure, light penetration, and soil and foliar characteristics in hemlock stands prior to arrival of the adelgid. Headwater stream quality is being monitored over a two year period to assess effects on aquatic and riparian invertebrates, and stream chemical and physical characteristics. Forest composition and structure will be correlated with topographic features to assess what factors put hemlocks most at risk for widespread mortality. Results will show land managers how post-adelgid forests will appear, determine characteristics of hemlock stands most at risk of widespread mortality, and prioritize resources to save our hemlocks. Mechanisms of hemlock resistance to the hemlock woolly adelgid are being investigated. Physical, mechanical and phenological differences of the highly susceptible eastern hemlock are being measured and compared to adelgid-resistant Asian and western hemlocks. Phenological differences, characteristics of the feeding site,sap viscosity and chemical composition are being assessed. A hemlock woolly adelgid-specific monoclonal antibody, coupled with an ELISA, is being used to assess the extent to which predators consume adelgids and potentially influence adelgid populations. Our research will help minimize the effects of this invasive species on hemlock resources.

In an effort to better understand the relationships that exist between forest-dwelling bats, nocturnal insects, and their forest environment, the forest entomology and wildlife ecology labs are comprehensively surveying these predator/prey groups in forests that vary in structure. We are isolating prey DNA from bat fecal material to more accurately assess bat consumption of insects. Prey DNA has been successfully isolated from bat feces, and selection of appropriate primers is underway to refine molecular identification. These results will help natural resource managers protect potentially endangered species.

Impact

Research on natural enemy recruitment by expanding populations of the exotic Asian chestnut gall wasp could lead to potential biological control of the gall wasp, minimizing its impact in commercial chestnut production and restoration efforts for the American chestnut. Herbivore susceptibility in chestnut has not been fully investigated. Our work on jasmonic acid-dependent defenses and the role of tannins in these defense responses enhances our understanding of chestnut-herbivore interactions and woody plant defenses, and also helps elucidate ecologically important species-specific and tissue-specific differences in tannin induction.

The effects of invasion by an exotic insect on an ecologically unique forest ecosystem are being evaluated. Long term monitoring plots to assess the effects of the exotic invasive hemlock wooly adelgid will help determine the characteristics of hemlock forests most at risk of widespread mortality, and help prioritize resources needed to save our hemlocks. Mechanisms of hemlock resistance to the invasive hemlock woolly adelgid are being investigated with the hope of employing some of these resistance mechanisms to save the eastern hemlock. Understanding the extent to which native natural enemies are able to exploit exotic invaders will provide additional tools for the development of viable management options, potentially minimizing the hemlock woolly adelgid's impact. Our research will help minimize the effects of this invasive species on our hemlock resources.

Evaluating the distribution and occurrence of insect prey of forest dwelling bats, and how this prey base varies with forest disturbance, is an essential step in bat conservation. This work has implications with respect to forest stewardship and will help natural resource managers protect potentially endangered species.

Publications

Cooper, W.R. and Rieske, L.K. 2007. Community associates of an exotic gallmaker, Dryocosmus kuriphilus, (Hymenoptera: Cynipidae) in eastern North America. Annals of the Entomological Society of America 100. 236-244.

Dillaway, D.N., Stringer, J.W., and Rieske, L.K. 2007. Light availability influences root carbohydrates, and potentially vigor, in white oak seedlings. Forest Ecology and Management 250, 227-233.

Dillaway, D.N., Stringer, J.W., and Rieske, L.K. 2008. Regenerative status of white oak (Quercus alba L.) advance regeneration affects response to increased light availability. Forest Ecology and Management (Submitted).

Dodd, L.E., Lacki, M.J., and Rieske, L.K. 2008. Variation in moth occurrence and the implications for foraging habitat of the Ozark big-eared bat. Forest Ecology and Management (Under revision).

Rieske, L.K. 2007. Success of an exotic gallmaker, Dryocosmus kuriphilus, on chestnut in the USA: a historical account. Invited submission for the Bulletin of the European and Mediterranean Plant Protection Organization. EPPO Bulletin 37, 172-174.

Rieske, L.K. and Dillaway, D.N. 2008. Response of two oak species to extensive defoliation: Tree growth and vigor, phytochemistry, and herbivore suitability. Forest Ecology and Management (Submitted).