The emerald ash borers’ steady tree-munching trek across Iowa now has reached Marshall and Tama Counties. They now have damaged trees in 55 Iowa counties, many of which haven’t faced a threat like this since Dutch elm disease spread through the state decades ago. The green metallic ash beetle, native to Asia, eats into the tree under the bark, cutting the trees’ food supplies. Woodpeckers like to eat the pests, which can leave scars on the trees. The latest sighting was near Le Grand. The pest spreads largely on firewood.