The Emerald Ash Borer information site says:
Emerald ash borer (EAB), Agrilus planipennis Fairmaire, is an exotic beetle that was discovered in southeastern Michigan near Detroit in the summer of 2002. The adult beetles nibble on ash foliage but cause little damage. The larvae (the immature stage) feed on the inner bark of ash trees, disrupting the tree’s ability to transport water and nutrients.
Since its discovery, EAB has killed tens of millions of ash trees in southeastern Michigan alone, with tens of millions more lost in Ohio, Illinois, Indiana, Pennsylvania, West Virginia, Missouri, Wisconsin, Virginia, Ontario, and Quebec. The Michigan Department of Agriculture page on the Emerald Ash Borer explains that the best way to stop the spread of EAB (and to avoid fines ranging from $1,000 to $250,000 and jail time of up to five years) is to not transport firewood. All types of firewood can transport invasive pests other than EAB including Beech Bark Disease, Asian Longhorned Beetle, Sirex Woodwasp, and Gypsy Moth.