Introduced basswood thrips, Thrips calcaratus Uzel has recently been associated with damage to American basswood, Tilia americana L., an important component of mixed northern hardwood forests. This insect is not known to cause damage to small-leafed linden, Tilia cordata,in its native European habitat. Objectives of this study are to assess relative populations of thrips and other herbivorous insects associated with basswood, to evaluate possible relationships between site factors and basswood health, and to determine the basis for differential levels of damage caused by T. calcaratus in its native and introduced range. Tree condition, insect populations and site conditions were monitored in twenty-two sites in the Great Lakes region. Defoliation, crown density, and branch dieback were estimated for basswood from 1998-2000. Branch dieback increased from about 7 to 17 percent and foliage transparency increased from about 22 to 33 percent. T. calcaratus accounted for over 95% of total insect abundance obtained from foliage samples. Differences in seasonality were observed among herbivorous thrips, with introduced species appearing earlier in the season when buds and young foliage were present, and native species occurring later in the season once foliage had matured. Occurrence of the native basswood thrips, Neohydatothrips tilae (Hood), coincided with the native predator, Leptothrips mali (Fitch). Data on thrips emergence and phenology of Tilia americana and T. cordata were obtained from sites in North America and Europe to determine whether differential T. calcaratus damage is related to differences in the degree of synchrony of thrips emergence with Tilia budbreak. Host association of T. calcaratus was tested using a laboratory bioassay and field seedling comparison of T. cordata and T. americana. Understanding the impacts of T. calcaratus may help develop general principles of invasion ecology and provide suggestions for management.
Species 1: Thysanoptera Thripidae Thrips calcaratus (introduced basswood thrips)
Keywords: exotic, forest
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA