emerald ash borer
Overview
The emerald ash borer (Agrilus planipennis), is a green jewel beetle native to north-eastern Asia. Females lay eggs in bark crevices, after hatching, larvae chew through the bark to the inner phloem where they feed and develop to emerge as adults in one to two years. The serpentine feeding galleries of the larvae disrupt the flow of nutrients and water, effectively girdling and thus killing the tree, as it is no longer able to transport sufficient water and nutrients to the leaves to survive. Adults begin to emerge from trees in late spring, after emergence, adults feed for one week on ash leaves in the canopy before mating. Females typical live six weeks and lay approximately 40–70 eggs. Emerald ash borer populations primarily spread through flight or by transportation of ash bark in such products as firewood or nursery stock. Such transport, allows the beetle to reach new areas and create satellite populations outside of the main infestation.
In its native habitat, it is typically found at low densities and does not cause significant damage to trees native to the area. Outside its native range, it is an invasive species and is highly destructive to ash trees native to Europe and North America. The insect was first identified in Michigan in 2002,[26] but it may have been in the U.S. since the late 1980s.[27] It is suspected that it was introduced from overseas in shipping materials such as packing crates.[26]The beetle has a core population in Michigan and surrounding states and provinces. Populations are more scattered outside the core area, and the edges of its known distribution range north to Ontario, south to northern Louisiana, west to Colorado, and east to New Brunswick. In eastern Europe, a population was found in Moscow, and has spread to far eastern Ukraine. From 2003 to 2016, this population has spread west towards the European Union at up to 40 km (25 mi) per year and is expected to reach central Europe between 2031 and 2036. Every North American ash species has susceptibility to emerald ash borer, after initial infestation, all ash trees are expected to die in an area within 10 years. The emerald ash borer threatens the entire North American genus Fraxinus. Emerald ash borer kills young ash trees several years before reaching their seeding age of 10 years.[8] In both North America and Europe, the loss of ash from an ecosystem could result in increased numbers of invasive plants, changes in soil nutrients, and effects on species that feed on ash.[10]
Extent and Impact Of Infestation
Ash trees are among the most valuable and abundant North American woodland trees with estimates of ash trees in the United States of between seven and nine billion with an estimated value of more than $280 billion. The emerald ash borer has destroyed 40 million ash trees in Michigan alone and tens of millions throughout other states and Canada. As of October 2018, the EAB was found in 35 states, and the Canadian provinces of Ontario, Quebec, New Brunswick, Nova Scotia and Manitoba.
Ash trees are especially abundant in eastern forests, but the mother lode of diversity is actually in the southwestern U.S., where at least eight of 16 native ash species occur. Cultivars of green ash, white ash and velvet ash have also been planted in landscapes and along roadways across the U.S. for decades. Because ash was so commonly propagated, nurseries sustained millions of dollars in losses when the EAB quarantines were imposed. Hundreds of millions of mature urban ash trees are growing on municipal and private land in the U.S. A 2010 analysis in Ecological Economics examined the potential costs of either treating or removing 50 percent of landscape ash trees in urban areas affected by EAB. Projected costs would exceed $10.5 billion by 2019. If suburban ash trees are included, costs nearly double.
Estimating costs of treatment or removal, however, does not do justice to the full economic impacts of losing ash trees, especially large trees, in residential and developed areas. Ash trees comprise up to 50 percent of the municipal trees growing along boulevards and in parks in some cities. Losing a substantial portion of mature trees dramatically alters the appearance of neighborhoods and diminishes property values. Stormwater run-off increases. Shade decreases, and air conditioners run longer. In southeast Michigan municipalities, water use soared as a result of widespread ash mortality, resulting in surcharges levied by the regional water authority. Green ash, the most widely distributed ash in the U.S., grows in many types of soils and is often abundant along rivers, streams and other waterways, as well as in forests. White ash is also widely distributed, frequently growing in mixed stands with oaks, maples and other hardwoods. Black ash occurs most commonly in swamps and bogs in the northern U.S. and parts of Canada, often in sites where it is the only tree present. Unfortunately, black ash is also a highly preferred host for EAB and very vulnerable — it generally takes fewer EAB larvae to kill black ash trees than similarly sized trees of other ash species. The long-term ramifications of ash mortality in forests and riparian settings are not yet known, but can be expected to cascade through ecosystems. Nutrient cycling, hydrology, composition of herbaceous plants and the habitat available for birds, mammals, insects and other animals are all likely to be affected.
Along with its ecological value, black ash has cultural and spiritual significance for many American Indian tribes from Minnesota to Maine, as well as First Nation tribes in Canada. Some tribes even trace their origin to a black ash tree that split — one fork became man and the other became woman. The art of black ash basketry has been handed down from generation to generation in many tribes. Cooperative efforts to collect and preserve ash seeds, including seeds from black ash trees, have been undertaken by a number of tribes, along with scientists from federal agencies and universities.
Asian ashes employ natural defenses to repel, trap, and kill emerald ash borer larvae. Although studies of American ashes have suggested that they are capable of mustering similar defensive mechanisms, the trees do not appear to recognize when they are under attack.[30] Many of the specialized predators and parasitoids that suppressed emerald ash borer in Asia are not present in North America. Several parasitoid species from Asia were released in North America with limited success. The USDA is also assessing the application of an insect fungal pathogen in conjunction with parasitoid wasps.[48]
Status Of A Solution
We have identified two candidate microbes and are working on a license to develop them for forestry applications. Further testing, proof-of-concept, and toxicology is required or different microbes may need to be discovered to address this pest.
