Emerald Ash Borer
Insects and Society By Crystal Moore
Introduction
Our ash trees are in peril. This peril is not because of climate change or deforestation. This peril is from a small, green, invasive insect called the emerald ash borer. Native to Asia, ash borers were first discovered in the United States in 2002. Since then, they have infested and killed tens of millions of trees. This has the potential to be the most expensive, and devastating, invasive species ever known in the U.S. These insects are changing entire forest ecosystems and are quickly spreading all over the country. But forestry officials and biologists are working to combat the invasion with ash insecticide treatments and releasing their predators, stingless wasps, into forests. The fate of our ash trees hangs in the balance.
Field of Study
Emerald Ash Borer and Forestry
The field of natural resources has a wide range of disciplines under its umbrella. The term natural resources refer to any material, substance, or intangible benefit that nature can provide and can also be used for economic benefit. One of the more intriguing disciplines within natural resources is wildlife conservation. This specialized discipline seeks to conserve habitat and species that suffer from declining numbers due to habitat fragmentation, poaching, climate change, and pollution.
Natural resources contribute to society in a myriad of ways. First, it provides the earth and its inhabitants with much-needed clean water and air sources. Second, it provides food sources to other species and humans in the form of plants and animals. Third, most construction materials for shelters are made from natural resources. Finally, it provides recreation to people and that translates into economic gains for recreation businesses reliant on tourism. There are many jobs available for those in the natural resource profession. Many graduates go on to become park rangers, forest managers, biologists, fish hatchery managers, mining supervisors, and eco-tourism guides.
This field of study relates to the decimation of forests by emerald borer beetles because hundreds of thousands of trees are at risk of death (Cipollini et al. 2018). This can potentially cause recreation to falter due to a lack of scenery. It can also affect a logging industry that relies on stands of trees to cut and sell to manufacturers (Wisconsin DNR 2020). More importantly, it could affect the ability of trees to sequester carbon from the atmosphere (American Forests 2013). This could lead to increased global and ocean warming.
Close-up of emerald ash borer
Critical Issue
The emerald ash borer beetle, also known as EAB, is native to Asia. The first known case of invasive species in the United States occurred in 2002. Since that time, EAB has spread to forests throughout the U.S., destroying ash tree stands in at least 18 states (American Forests 2013). In Southeast Michigan, more than 60 million ash trees have been killed since 2002. The main victims of EAB are white ash, green ash, and black ash (American Forests 2013). This may yet become the most destructive pest invasion ever in the United States.
The major die-off of trees is a significant environmental problem and a potential threat to humanity. In the past 19 years, 60 million ash trees have not been available to sequester carbon (American Forests 2013). The ash trees have not had long enough to evolve resistance or defense against the ash borer beetles. Carbon dioxide is linked to climate change, acidification of the oceans, and unhealthy air quality (Bushaj et al. 2020). It also would have a large economic impact. There are an estimated 8 billion ash trees in the U.S. and their worth is estimated at 280 billion dollars. If a significant percentage of ash trees are removed, it may change the forest landscape and cost the logging or ecotourism industry billions of dollars (Bushaj et al. 2020).
The most common position of opposition against treating ash trees with insecticide to kill ash borer beetles is the unknown effects on other species in that given habitat (Liu 2018). Insecticides, even in diluted amounts, have the potential to kill native insects, amphibians, and reptiles.
Featured Insect
Emerald Ash Borer Beetle
Emerald ash borers (Agrilus planipennis) are a species of beetle invasive to the United States. These beetles are part of the order Coleoptera and the family Buprestidae (Wisconsin DNR 2020). The native range of these beetles spanned much of the upper and eastern Asian continent. They were likely brought through shipping or trade and have been identified in over 18 states (American Forests 2013). They are found in woody areas, mostly in the eastern part of the United States. with species of ash trees. The emerald ash borer lives and feeds on the inner bark of white and black ash trees. This is fatal to the trees it infects in the United States because they haven’t had enough time to evolve a resistance to the infestation (USDA 2015). The beetles feed on the phloem, a type of respiratory system, and disrupt the flow of nutrients to up the tree’s vascular system; this eventually kills it. The emerald ash borer larvae make a series of s-shapes that can be seen once the inner bark is exposed (Liu 2018). When the larvae are ready to emerge, they create a d-shaped hole in the ash tree (Liu 2018).
The lifecycle of an emerald ash borer lasts approximately one year. Adult female ash borers insert up to 90 eggs in the bark of living and healthy ash trees The eggs are very small-only 1/15 of an inch in diameter (USDA APHIS 2019). Once the eggs hatch, the insects enter the larvae stage. This is where they really become destructive as they bore into the vascular system of the phloem and create the infamous zigzag or s-shape (American Forests 2013). The larvae are light brown in color and will reach up to an inch long when mature. They spend months feeding on the tree and can tolerate frigid temperatures. In April the larvae will pupate and transform into adult borer beetles (Wisconsin DNR 2020). The process of pupal development takes approximately one month. When the adults emerge, they are approximately ½ inch long. They have a metallic-green coloration that shimmers in certain light conditions (Liu 2018). The mature adults live for approximately three weeks (Wisconsin DNR 2020). They use this time to find mates and insert eggs in a suitable ash tree host.
Biologists have discovered that emerald ash borer beetles have at least four insect enemies. Currently, there are four stingless wasps that will attack both larvae and eggs. They are Spathius galinae, Oobius agrili, Spathius agrili, and Tetratischus planipennisi (American Forests 2013). Some of these wasps have already been released into known affected areas to test this biological control (USDA APHIS 2019).
Insect and Human Connection
EAB is most destructive to ash trees when it is in its larval life cycle. True to their name, borers feed through the inner bark and phloem (Liu 2018). Phloem is the living tissue from which ash trees receive nutrients. These larvae cut off nutrients to the tree and they die anywhere from 2-3 years after infestation (American Forests 2013). All species of ash in North America are in danger of Emerald Ash Borer infestation, but the hardest-hit states are in the east and midwest (Cipollini et al. 2011). The emerald ash borer infestation in North America has forced a collaborative relationship between entomologists, landowners, and government organizations like the U.S. Forest Service. It was first detected in 2002 in Michigan but has likely been in the country longer (Cipollini et al. 2011). These agencies are working together to try containment and eradication of EAB through a variety of management strategies (Liu 2018).
The relationship between landowners, entomologists, and government officials can be strained because of differences in the perceived value of ash tree conservation. No one group benefits from the interactions if all three do not agree on a plan of action in a cohesive manner. Many state and city governments realize the potential disaster from such a loss of tree cover and some offer benefits for landowners in the fight against ash borers (Liu 2018). For example, the state of Virginia offers to help pay up to 50% of the costs associated with treating infested ash trees (Virginia Department of Forestry 2021). In New York, there is no grant to help pay for treatment or removal of the trees. Landowners have balked at the treatment program grant, and this has resulted in many trees not being treated (NYS Department of Conservation 2021). However, not all interactions between scientists, the public, and government officials have a negative outcome. In Pennsylvania, a model plan for mitigation was proposed and passed by stakeholders in the state (Liu, 2018). This is a positive outcome in the long battle with the emerald ash borer because different invested parties were able to form a plan of action.
EAB’s presence negatively affects humans. The spread of the emerald ash borer has resulted in the loss of millions of dollars worth of the tree’s value. The cost to treat or remove an ash tree is expensive. In New York, there is no grant program to help owners remove infested trees: the average cost is approximately 2,000 dollars per tree (NYS Department of Conservation 2021). Urban areas and rural areas alike have had to budget for the removal and treatment of trees since 2002 (Bushaj et al. 2020). This is budget money allocated towards treating infestations of EAB could be spent improving infrastructure, social justice programs, intervention programs, and mental health programs. The cost of the emerald ash borer has taken away resources that could serve positive purposes for humans.
Agrilus planipennis, or EAB, is native to East Asia and has been spread unintentionally by humans. International shipping likely brought the invasive insect to the United States, and it has been well-suited to adapt to its new environment. Unfortunately, the ash trees in North America have not had time to acquire adaptations or resistance to these invaders as the ash trees of Asia have (Cipollini et. al 2011). Science and technology are needed to help the ash trees survive. Plans are being made in some states to release predatory wasps to counteract the devastation of the ash borers. Four stingless wasps are known to prey on emerald ash borers and have not shown evidence of negatively affecting the habitat (American Forests 2013). This has the potential to save ash trees from the infestations that are changing the forest landscape of the country.
