Emerald Ash Borer
The emerald ash borer (Agrilus planipennis) is a small beetle native to Asia, where the population is in a natural balance. It was discovered in North America for the first time in 2002 and has since caused the loss of about 100 million ash trees in Ontario and the United States.
It’s the tunnels dug under the bark during the larval stage that impede the flow of sap and cause the complete decline of infested trees in 2-4 years. The emerald ash borer is undoubtedly the worst threat that the urban forest has known since the outbreak of Dutch elm disease in the 1970s. The adult borer is a small insect emerald green color that has the ability to fly, but that moves little. It feeds on ash leaves of all species and mates plenty to laying eggs on the bark, preferably in the grooves where the eggs will be safe until they hatch.
The larvae that emerge, tiny at first, will penetrate under the bark to feed on the inner bark tissue by digging winding galleries for several months. The larvae will then dig deeper into the woods and turn on themselves to begin the metamorphosis into the adult stage. At the awakening, adults pierce the bark to emerge, resulting in finely cut holes in the shape of a “D” and characteristic of the EAB, called exit holes. Although the insect can fly for several kilometers at the adult stage, the study of its behavior has demonstrated that it is rather sedentary, as long as food and habitat were abundantly available. Females even tend to nest on the same tree in which they developed. An important factor in the spread of the EAB is the subtlety of its presence. Symptoms usually take 2 years to develop, and then, infested trees are dying very quickly. The beetle generally kills its host in 3 or 4 years.
In several infested cities, municipal authorities have discovered this pest only when several ash trees had to be destroyed simultaneously. The beetle raged for a few years and had time to spread over a large area. It is often too late to contain the infestation, but the valuable ash trees can be saved if treated before they show important symptoms of dieback.