Distribution of American Beech (Fagus grandifolia) and Beech Scale (Cryptococcus fagisuga Lind.) in Michigan from 2005 to 2009

摘要

Beech scale (Cryptococcus fagisuga Lind.) (Hemiptera; Coccidae), an invasive insect associated with beech bark disease, was discovered in 2000 in a localized area of northwest Lower Michigan and one area in the eastern Upper Peninsula. From 2005 to 2009, we surveyed 809 sites in 73 Michigan counties to determine whether American beech (Fagus grandifolia) trees were present and, if so, whether trees had been colonized by beech scale. Beech trees were present in 696 sites in forest, recreation, and residential areas. By 2009, beech scale had infested beech trees in 8 of 15 counties in the Upper Peninsula, 14 of 68 counties in the Lower Peninsula, one of three islands in Lake Michigan, and all three sampled islands in Lake Huron. Colonization of islands more than 20 km from infestations on the mainland suggest that beech scale was likely introduced by humans or birds. Rates of expansion of 12 discrete beech scale populations varied from 3.3 to 14.3 km per year.