The Emerald Ash Borer (EAB) is a highly destructive invasive beetle native to Asia that poses a significant threat to ash trees across North America. This metallic green insect was accidentally introduced and first discovered in Michigan in 2002. The beetle’s larvae feed aggressively under the bark, eventually killing the host tree within two to four years. Understanding the two primary ways this pest disperses is necessary to curb its rapid expansion and protect remaining ash populations.
Local Spread Through Adult Flight
The natural movement of the Emerald Ash Borer occurs when adults emerge from an infested tree and fly to a new host to mate and lay eggs. They are generally active on warm, sunny days and feed briefly on ash leaves before seeking a mate. This natural dispersal is relatively slow and predictable compared to human-assisted spread. Most beetles fly short distances, often less than one-half mile from their emergence point. This flight capability contributes to the slow, steady expansion of an infestation into neighboring woodlots and communities.
Long-Distance Spread Via Human Transportation
Human activity is the most significant factor driving the rapid, long-distance spread of the Emerald Ash Borer. EAB can travel hundreds of miles when people unknowingly transport infested materials, allowing the beetle to bypass natural barriers and jump far ahead of its natural expansion front. The primary vector for this rapid spread is the movement of ash firewood, which can harbor the pest in any life stage beneath the bark. Other infested ash products, including unprocessed logs, nursery stock, and wood packaging materials, also facilitate long-range movement. This transportation creates new, isolated “satellite” infestations, leading governmental agencies to implement regulations and quarantines to restrict the movement of ash wood.
The Hidden Threat: Larvae in Ash Products
Moving ash wood is dangerous because the EAB spends the majority of its life cycle, typically one to two years, as a larva hidden beneath the bark. The female beetle lays her eggs in bark crevices, and the larvae bore into the phloem layer, the inner bark tissue responsible for transporting nutrients. This feeding activity effectively girdles the tree, cutting off the flow of nutrients and water, which leads to the tree’s death. Since the larvae are internal, transporting infected wood unknowingly moves a hidden, active infestation to a new location. The inability to easily detect this life stage makes public awareness regarding the movement of ash wood products a major factor in slowing the spread of the pest.