‘Agrilus planipennis feeds on ash trees in the Northern Hemisphere’ doesn’t sound as menacing as it should. Agrilus planipennis is the scientific name for the Emerald Ash Borer – a brilliantly green jewel toned beetle species native to northeastern Asia that uses ash trees as their personal breeding and feeding grounds.
Adult females, which feed on the leaves of ash trees, lay eggs in the cracks and crevasses of the bark. Once the eggs hatch approximately two weeks later, the larvae feed underneath the bark gathering strength and slowly killing the tree from the inside. The baby borers create serpentine-like tendrils in the tree and disrupt the flow of photosynthesised nutrients and water to the leaves by viciously attacking the phloem, cambium and xylem — three components of tree tissue which are vital to a tree’s survival. The baby borers then remain in the tree for one to two years before they emerge as adults, chewing their way out.
Scientists estimate that the species became prevalent in northern Michigan nearly 15 years ago, being introduced accidentally through shipping materials, such as wooden crates. Previous to being discovered as a threat, little was known about the beetles. In northeastern Asia, their place of origin, the borer is found at lower densities and as a result, do not cause significant damage to native trees. Outside its native range, however, the borer is a predator; an invasive species that destroys the trees they inhabit and disrupts the forest’s ecosystem.
In Canada alone, the borer has killed upwards of tens of thousands of ash trees, with the remaining at risk of death. It’s hard to visualize the effects that the beetle has actually had. To put it into perspective, the disappearance of ash trees can act like a sink hole to forest ecosystems. Their disappearance can cause soil erosion into streams because of root loss; gaps in the tree canopy result in warmer water temperature because of solar exposure; biodiversity of herbivores relying on the trees for food decrease and instead, invasion of plant species, originally kept at bay, grow and take hold, thriving on the rise in the forests climate; and a new cyclical pattern emerges as the Emerald Ash Borer leaves devastation and destruction of our forests in its wake.
Without population control from predators, parasitoids or resistant trees that exist in Asia, the borer species continues to grow and cause further damage to our vulnerable Ash species here in Canada. Recently, Canadian scientists have lab-raised Tetrastichus planipennisi, a non-stinging wasp species native to Asia and a natural enemy against the borer, as part of a ‘bio-control’ large-scale attempt to manage the borer population. The idea behind these wasps is that the females lay eggs within the borer larvae and once the wasps’ eggs hatch, they will feast on the larvae of the borers themselves, thereby killing them. Interestingly, the wasps are native to China and, according to researchers, have no effect on humans or the surrounding ecosystem here in North America. The wasps continue to be released into Ontario and Quebec in an effort to curb the death of our ash trees.
Nearly every province has taken serious measures to ensure the extermination of the Emerald Ash Borer from our trees. The borers’ ample determination to keep its title as one of the most threatening invasive species remains, however with building pressure to decline the borer’s home and new innovative ways to trap and attack the borer, the ash trees of North America will hopefully one day make a speedy return.