Comparisons of arthropod and avian communities in insecticide-treated and untreated hemlock stands in Great Smoky Mountains National Park

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Josephine Fields Falcone (Creator)
Western Carolina University (WCU )
Web Site:
Laura DeWald

Abstract: Great Smoky Mountains National Park is using systemic imidacloprid in Hemlock Conservation Areas to treat eastern hemlocks (Tsuga canadensis) infested with hemlock woolly adelgid (Adelges tsugae, HWA). The purpose of this study was to investigate the effects of systemic imidacloprid treatments on the insectivorous bird community and on the hemlock canopy arthropod community in the context of food availability for insectivores. Territory mapping of three hemlock-associated Neotropical migratory foliage-gleaning bird species was conducted in six pairs of treated and untreated hemlock study sites. Relationships between bird territory density and hemlock foliar density were also examined. Canopy arthropods were sampled in these paired sites by clipping mid-canopy hemlock branches. Arthropods were identified to order except Hemiptera to suborder. Arthropods were further categorized into focal bird prey guilds and non-target herbivorous insect guilds. Focal bird densities did not differ between treated and untreated sites but were positively related to branch foliage mass, implying a preference in these birds for well-foliated hemlocks. There was no difference in HWA infestation between treated and untreated sites, indicating that treated hemlock trees were not sampled at peak efficacy of imidacloprid treatments. Over 900 non-HWA arthropods from 16 orders were collected. There were no differences in richness, abundance, composition, or density between treated and untreated sites for total arthropods or for the two focal bird prey guilds arthropods = 3 mm and larvae = 3 mm, revealing little impact on the overall arthropod crop from imidacloprid treatments. However, non-target herbivorous Hemiptera and larval Lepidoptera were significantly reduced in treated hemlocks. Although larval Lepidoptera are primary prey for focal birds, lack of differences in bird densities suggests the birds are finding other food resources in these mixed hemlock-deciduous stands. Results of this study indicate that controlling HWA-induced defoliation through use of imidacloprid may in the short term benefit hemlock-associated birds. However, while imidacloprid treatments did not appear to affect most non-target arthropods, guilds of non-target herbivorous insects should be monitored for long-term declines.

Additional Information

Language: English
Date: 2009
canopy arthropods, eastern hemlock, hemlock woolly adelgid, imidacloprid, Neotropical migratory birds, non-target effects
Hemlock woolly adelgid -- Control -- Great Smoky Mountains National Park (N.C. and Tenn.)
Birds -- Great Smoky Mountains National Park (N.C. and Tenn.)
Arthropoda -- Great Smoky Mountains National Park (N.C. and Tenn.)

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