Search research reports:
Exotic Organisms Interact to Influence Persistence of a Native Species: Potential Interplay Between the Asian Chestnut Gall Wasp and Its Chestnut Hosts
Department of Entomology
The Asian chestnut gall wasp is an exotic invader that causes round, 8-15 mm diameter, greenish-red leaf and twig galls on all chestnut species, though differences in susceptibility differ among various chestnut species and varieties. The gall wasp was accidentally introduced into North America in 1974, and has become a serious pest of chestnut worldwide. Galls suppress shoot and twig growth, reduce tree vigor and wood production, and reduce fruiting and nut yield. Severe infestations can kill trees.
In the past American chestnut was a dominant component of hardwood forests of eastern North America. The accidental introduction of the chestnut blight fungus in 1904 virtually eliminated American chestnut from its former range. Today American chestnut persists as a blighted, non-flowering shrub that dies back when it reaches 2-3 m. In addition, Chinese chestnut are commonly used in ornamental and landscape plantings, and Chinese, Japanese, and European chestnut, and their hybrids, are cultivated for nut production, providing plentiful host material as the gall wasp expands its geographic range.
Extensive efforts at developing blight-resistant varieties have met with some success. Hybridization with blight-resistant Chinese chestnut, followed by repeated backcrossing, produce blight-resistant chestnut. These blight-resistant hybrids are appearing in restoration programs aimed at restoring American chestnut to the landscape, and in addition to other stressors, will be interacting with expanding Asian chestnut gall wasp populations. These interactions will undoubtedly affect chestnut production and American chestnut restoration efforts in eastern North America.
The overall goal of this research is to evaluate the geographic range expansion of D. kuriphilus in North America, the effects and ecological associations that have developed as D. kuriphilus extends its geographic range, and species-specific and varietal differences in Castanea susceptibility to the gall wasp, including qualitative and quantitative differences in source strength and signaling compounds.
The specific objectives are to
1) evaluate population characteristics of the Asian chestnut gall wasp, Dryocosmus kuriphilus, and its natural enemy recruitment, near the edges of its known geographic range in North America,
2) evaluate the extent to which its Castanea hosts influence gallmaker success via qualitative and quantitative differences in source strength, and
3) the extent to which its Castanea hosts influence qualitative and quantitative differences in plant signaling.
2011 Project Description
Non-native invasive species continue to threaten Kentucky's forest sustainability and productivity. The hemlock woolly adelgid is an exotic invasive herbivore that kills hemlocks and was first reported in Kentucky in 2006. The role of eastern hemlock in headwater stream riparian zones is being investigated. We are also evaluating natural enemies and mechanisms of hemlock host plant resistance.
In addition, American chestnut restoration efforts and chestnut production are under threat from the invasive Asian chestnut gall wasp. Geographic range expansion of the gall wasp is being documented, as is recruitment of native and introduced natural enemies.
In collaboration with the Wildlife Ecology lab in the Department of Forestry, fecal samples from Rafinesque's big-eared bat were field collected and DNA-based analysis of diet is progressing. Techniques to determine nutritive content of prey Lepidoptera (bomb calorimetry) is under development.
Exotic species affect native taxa, alter ecological interactions, and potentially alter ecosystem function. Eastern hemlock riparian zones support more abundant, taxa-rich benthic macroinvertebrate communities. The shredder guild is more abundant in hemlock streams, perhaps because eastern hemlock litter input is more consistent throughout the growing season. The effect of varying litter input on benthic macroinvertebrates is under further investigation. Four terrestrial arthropod taxa, Isopoda, Diplopoda, Formicidae, and Staphylinidae, are more abundant in deciduous dominated riparian zones.
The predator Laricobius nigrinus is effective against hemlock woolly adelgid and demonstrates a positive functional response that is not affected by hemlock species. The amount of adelgid consumed by L. nigrinus does not differ between eastern, western, and Chinese hemlock. Resistance to the hemlock woolly adelgid varies across hemlock species, and the mechanism of this resistance also varies. Among the resistant Asian hemlocks, Chinese hemlock is unsuitable at all stages of adelgid development, whereas the northern Japanese hemlock is initially acceptable, but is not suitable for complete adelgid development.
The Asian chestnut gall wasp is now found in eleven states in the U.S. Eight previously unreported parasites have been collected, and an introduced parasite is well established. Fecundity of adult females declines with age, as does the size of individual eggs (a measure of fitness). Interactions between the gall wasp and a stem cankering fungus reduces the fitness of the host, enhances the fitness of the fungus, but has no impact on gall wasp fitness.
Clark, J.T., S. Fei, L. Liang, and L.K. Rieske. 2012. Mapping eastern hemlock: Comparing classification techniques to evaluate susceptibility of a fragmented and valued resource to an exotic invader, the hemlock woolly adelgid. Forest Ecology and Management 266: 216-222.
Cooper, W.R. and L.K. Rieske. 2011. Chestnut species and jasmonic acid treatment influence development and community interactions of galls produced by the Asian chestnut gall wasp, Dryocosmus kuriphilus. Journal of Insect Science 11:140; available online: insectscience.org/11.140.
Dodd, L.E., M.J. Lacki, and L.K. Rieske. 2011. Habitat associations of Lepidoptera in the Ozark Mountains of Arkansas. Journal of the Kansas Entomological Society. page numbers not avail.
Spaulding, H.L. and L.K. Rieske. 2011. A glimpse at future forests: predicting the effects of Phytophthora ramorum on high-risk forests of southern Appalachia. Biological Invasions 13: 1367-1375.