Invasive Species Information
The Emerald Ash Borer, Agrilus planipennis, Fairmaire (Coleoptera: Buprestidae), commonly referred to as "EAB", is an invasive wood-boring beetle. Native to Asia, the beetle's first North American populations were confirmed in the summer of 2002 in southeast Michigan and in Windsor, Ontario. EAB was likely introduced to the area in the mid-1990's in ash wood used for shipping pallets and packing materials in cargo ships or shipping containers. Emerald Ash Borers feed on and eventually kill all native ash trees (Fraxinus spp.). Slowing their spread is imperative.
Since its introduction into North America, 18 states (Connecticut, Illinois, Indiana, Iowa, Kentucky, Kansas, Maryland, Massachusetts, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and Wisconsin) and two Canadian provinces; Ontario and Quebec. EAB was first confirmed in New York in June 2009 near Randolph, in western Cattaraugus County.
The natural spread of EAB infestations in North America is about 2 miles per year, depending on the infestation intensity. However, the rapid spread of the beetle through North America is most likely due to the transport of infested firewood, ash nursery stock, unprocessed ash logs, and other ash products. In an effort to slow the continued spread of EAB, both Federal and State agencies have instituted quarantines of infested areas to regulate the transport of ash products.
The Emerald Ash Borer (Agrilus planipennis) is an Asian wood-boring beetle in the family Buprestidae. This beetle was accidentally introduced to North America around the beginning of the 21st century (first noted in both Michigan, U.S.A., and Ontario, Canada, in 2002). Since then, it has killed millions of ash trees (Fraxinus spp.) in (at least) Michigan, Indiana, Illinois, Ohio, Pennsylvania, Maryland, West Virginia, and Wisconsin (U.S.A.) and Ontario and Quebec (Canada). Emerald ash borers colonize trees that range in size from saplings to fully mature trees. Larvae feed under the bark on phloem and outer xylem, girdling and killing trees within 1 to 4 years of colonization. Efforts to find one or more effective biocontrol agents are ongoing, but the potential ecological and economic costs of this pest are clearly enormous. (Poland and McCullough 2006; Duan et al. 2009; Gandhi and Herms 2010; Kovacs et al. 2010)
Regularity: Regularly occurring
Type of Residency: Year-round
The native range of the Emerald Ash Borer includes China, Japan, Korea, Mongolia, the Russian Far East, and Taiwan (Anulewicz et al. 2008 and references therein).
Anulewicz et al. (2008) carried out field experiments to examine the potential for Emerald Ash Borers in North America to expand their host range to include species other than ashes (Fraxinus spp.). In Asia, the Emerald Ash Borer seems not to be a major pest, generally occurring at low densities and attacking severely stressed or declining trees. In North America, however, where ash species have no co-evolutionary history with this insect, the Emerald Ash Borer has killed healthy, as well as stressed, Green Ash (F. pennsylvanica), White Ash (F. americana), Black Ash (F. nigra), and Blue Ash (F. quadrangulata). In Asia, Emerald Ash Borer has been reported to attack other hosts in addition to ashes, but attacks on non-ashes have not been reported for North America (although tens of millions of ash trees have been attacked). In field tests using several North American relatives of reported non-ash hosts from Asia, Anulewicz et al. found that, although Emerald Ash Borer adults would occasionally land on and oviposit on logs and trees of non-ash species, larvae did not successfully develop on anything other than ashes. (Anulewicz et al. 2008 and references therein)
Rebek et al. (2008) tested the resistance to Emerald Ash Borer of an Asian ash species, Manchurian Ash (Fraxinus mandshurica) and found that it was significantly less susceptible to Emerald Ash Borer attack than were tested North American ashes, suggesting the existence of targeted defenses resulting from a shared evolutionary history in their native Asia. Liu et al. (2007) reported that in China exotic North American species such as Green Ash are more susceptible to Emerald Ash Borer attack than are native Chinese ash species when planted at the same site.
Liu et al. (2007) studied two natural enemies of Emerald Ash Borer, Oobius agrili (Encyrtidae) and Tetrastichus planipennisi (Eulophidae), and found that both contribute significantly to Emerald Ash Borer population suppression on Green Ash in northeastern China. Previous studies showed that T. planipennisi was also an important mortality factor for Emerald Ash Borer on Manchurian Ash in China. Oobius agrili is a newly described solitary egg parasitoid of Emerald Ash Borer from China with no other known hosts. Although host resistance to Emerald Ash Borer differs between native Chinese ash species and species introduced from North America, the ability of these parasitoids to locate and attack Emerald Ash Borers apparently does not differ between Chinese and North American ashes. Based on the high observed parasitism rates, short generation times, high reproduction rates, and life-cycle synchronizations with their respective host stages, the authors suggest that these parasitoids may prove useful for biological control of Emerald Ash Borer in North America. (Liu et al. 2007 and references therein)
Yang et al. (2008) carried out no-choice tests to examine the potential host range of Spathius agrili (Hymenoptera: Braconidae), a braconid species described in 2005 that paralyzes Emerald Ash Borer larvae when it lays eggs on them, arresting their development, with newly hatched wasp larvae consuming the host beetle larva in 7 to 10 days (Yang et al. 2005). They found that although S. agrili can parasitize some other Agrilus larvae, observed attack rates were significantly lower than for its natural host, the Emerald Ash Borer.
Ulyshen et al. (2010) studied competitive interactions betwee two of the three hymenopteran parasitoids native to China that are being released in the United States as biological control agents for the Emerald Ash Borer, the larval ectoparasitoid Spathius agrili (Braconidae) and the larval endoparasitoid Tetrastichus planipennisi (Eulophidae) (the third species being released, Oobius agrili [Encyrtidae], is an egg parasitoid and therefore not expected to compete directly with the other two). Female S. agrili permanently paralyze their hosts by envenomation during oviposition and produce 1 to 18 offspring per host (mean 8.4); in China, they complete up to four generations a year and levels of parasitism range from 30% to 90%, with 1 to 35 eggs associated with a single host individual (Yang et al. 2005). Between 4 and 172 T. planipennisi offspring are produced per host (Uyshen et al. 2010). In contrast to larvae parasitized by S. agrili, host larvae parasitized by T. planipennisi remain active and continue to feed for about a week. After consuming the host larva, parasitoid larvae exit from the integument and pupate within the beetle gallery. Adult wasps eclose approximately 15 days after pupation and exit the tree through one or more holes chewed through the bark. In China, four or more generations are produced each year and observed levels of parasitism range from 0% to 65%, with 56 to 92 individuals developing in a single host larva (Liu et al. 2007; Yang et al. 2006). In competition trials, Ulyshen et al. (2010) found that S. agrili tended to excluded T. planipennisi, an observation they attribute to S. agrili being much more efficient at locating hosts. They also found that S. agrili parasitized larvae previously parasitized by T. planipennisi, although the reverse was not observed. However, S. agrili offspring failed to complete development on hosts that were previously parasitized by T. planipennisi. Ulyshen et al. (2010) suggested releasing these two species separately in time or space to avoid the antagonistic interactions observed in their study.
Although investigations of biocontrol options are focused on the use of parasitoids imported from China, Duan et al. (2009) surveyed the parasitoids currently attacking Emerald Ash Borer in western Pennsylvania. Five parasitoids were identified: Balcha indica (Eupelmidae), Eupelmus pini (Eupelmidae), Dolichomitus vitticrus (Ichneumonidae), and 2 ichneumonids identified only to genus, Orthizema sp. and Cubocephalus sp.. Together, these parasitoids parasitized 3.6% of the sampled Emerald Ash Borers (1,091 larvae, prepupae, and/or pupae). Balcha indica accounted for 82% of the parasitoids recovered. The association with Emerald Ash Borer of the two eupelmids, although not the ichneumonids, was confirmed in laboratory assays The authors suggest that these two eupelmid species may be complementary to the ongoing Emerald Ash Borer biological control efforts in the U.S., which include 1 egg and 2 larval parasitoids that attack Emerald Ash Borer in China (Liu et al. 2007; see above). Another native ectoparasitoid found to attack Emerald Ash Borer larvae, Atanycolus hicoriae (Braconidae) is being evaluated as a potential biocontrol agent as well. (Duan et al. 2009 and references therein)
Gandhi and Herms (2010) investigated the question of whether the large scale destruction of ashes (Fraxinus spp.) by Emerald Ash Borers in North America could result in the decline or extinction of other ash-associated arthropods.Their literature survey revealed that 43 native arthropod species in six taxonomic groups (Arachnida: Acari; Hexapoda: Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera) are known to be associated only with ash trees for either feeding or breeding purposes and are therefore at high risk. Most of these species are gall-formers, followed by folivores, subcortical phloem/xylem feeders, sap feeders, and seed predators. Another 30 arthropod species are associated with 1 to 2 host plants in addition to ash; herbivory on these hosts may increase as these arthropods shift from declining ash trees.
Life History and Behavior
In southeast Michigan, adult beetles emerge from host trees from late May through early September. Eggs are deposited singly in crevices and furrows on the outer bark of host trees. Upon eclosion, first instars immediately tunnel through the bark and begin feeding on phloem and outer xylem as they create serpentine, frass-packed galleries that impede translocation of water, nutrients, and photosynthate through the tree. Most individuals complete their life cycle in 1 year; however, a proportion of the population takes 2 years to complete development. (Rebek et al. 2008 and references therein)
Molecular Biology and Genetics
Statistics of barcoding coverage: Agrilus planipennis
Public Records: 0
Specimens with Barcodes: 7
Species With Barcodes: 1
National NatureServe Conservation Status
Rounded National Status Rank: NNR - Unranked
Relevance to Humans and Ecosystems
Kovacs et al. (2010) modeled Emerald Ash Borer spread and infestation over the period 2009 to 2019. They estimated the discounted cost of the treatment, removal, and replacement of ashes infested by Emerald Ash Borer on developed land within communities in a 25-state study area centered on Detroit. An estimated 38 million ash trees occur in this area. Their simulations predicted an expanding Emerald Ash Borer infestation that will likely encompass most of the 25 states and warrant treatment, removal, and replacement of more than 17 million ash trees with a mean discounted cost of $10.7 billion. They note that expanding the land base to include developed land outside, as well as inside, communities nearly doubles the estimates of the number of ash trees treated or removed and replaced, and hence the associated cost. The authors argue that estimates of discounted cost suggest that a substantial investment might be efficiently spent to slow the expansion of isolated Emerald Ash Borer infestations to postpone the ultimate costs of ash treatment, removal, and replacement. Although many uncertainties could change assumptions underlying the predictions of this analysis, it nevetheless provides some sense of the scale of the economic threat of the Emerald Ash Borer.
Emerald ash borer
The emerald ash borer (Agrilus planipennis) is a green beetle native to Asia and Eastern Russia. Outside its native region, the emerald ash borer (also referred to as EAB) is an invasive species, and emerald ash borer infestation is highly destructive to ash trees in its introduced range. The emerald ash borer was first discovered in America in June 2002 in Michigan. It was accidentally brought to America in the ash wood which was used in shipping materials.
The natural range of the emerald ash borer is eastern Russia, northern China, Japan, and Korea. It is invasive outside of its native range. Its first confirmed North American detection was in June 2002 in Canton, Michigan. It is suspected, that it was introduced by overseas shipping materials. It has since been found in several other parts of the North America. Ohio, Minnesota, and Ontario have experienced emerald ash borer migration from Michigan, and the species has continued to spread across the continent.
The French priest and naturalist Armand David collected a specimen of the emerald ash borer during one of the trips he took through imperial China in the 1860s and 1870s. He found the beetle in Beijing and sent it back to France, where a brief description by the entomologist Leon Fairmaire was published in the Revue d'Entomologie in 1888.
EAB primarily infest and cause significant damage ash species including green ash, black ash, white ash, and blue ash in North America. In its native range, emerald ash borer is only a sporadic pest on native trees as population densities typically do not reach levels lethal to healthy trees. Damage can occur in infested trees due to larval feeding. The serpentine feeding galleries of the larvae disrupt the flow of nutrients and water and can girdle the tree. On susceptible species or in the absence of organisms that suppress emerald ash borer populations, the tree will eventually no longer be able to transport sufficient nutrients to survive. EAB has also been found infesting White fringetree, but it was not apparent whether the trees were healthy when first infested, or were already in decline due to drought.
The emerald ash borer life cycle can occur over one or two years depending on the time of year of oviposition, the health of the tree, and temperature.
Adult beetles are typically bright metallic green and about 8.5 millimeters (0.33 in) long and 1.6 millimeters (0.063 in) wide. Underneath the elytra, the upper side of the abdomen is coppery-red, which is a distinctive feature of the species. After 400-500 accumulated growing degree days (GDD) at base 10 °C (50 °F), adults begin to emerge from trees, and peak emergence occurs around 1000 GDD. After emergence, adults feed for one week on ash leaves in the canopy before mating, but cause little defoliation in the process. A typical female can live around six weeks and lay approximately 40–70 eggs, but females that live longer can lay up to 200 eggs.
Eggs are deposited between bark crevices, flakes, or cracks and hatch about two weeks later. Eggs are approximately 0.6 to 1.0 millimeter (0.024 to 0.039 in) in diameter, and are initially white, but later turn reddish-brown if fertile. After hatching, larvae chew through the bark to the phloem and cambium where they feed and develop. Emerald ash borer has four larval instars. By feeding, larvae create long serpentine galleries. Fully mature fourth-instar larvae are 26 to 32 millimeters (1.0 to 1.3 in) long. In fall, mature fourth-instars excavate chambers in the sapwood or outer bark where they fold into a J-shape. These J-shaped larvae shorten into prepupae and develop into pupae and adults the following spring. To exit the tree, adults chew holes from their chamber through the bark, which leaves a characteristic D-shaped exit hole. Immature larvae can overwinter in their larval gallery, but can require an additional summer of feeding before emerging as adults the following spring.
EAB as an invasive species
Outside its native range, emerald ash borer is an invasive species, that is highly destructive to ash trees in its introduced range. Since its accidental introduction into the United States and Canada in the 1990s and its subsequent detection in 2002 in Canton, Michigan, it has since been found in several other parts of the North America. Ohio, Minnesota, and Ontario have experienced emerald ash borer migration from Michigan, and has continued to spread across the continent.
Invasiveness and spread
Without factors that would normally suppress EAB populations in its native range (e.g., resistant trees, predators, and parasitoid wasps), EAB populations can quickly rise to damaging levels. After initial infestation, all ash trees are expected to die in an area within 10 years without control measures. All North American ash species show susceptibility to EAB as North American species planted in China also show high mortality due to EAB infestation, but some Chinese species show resistance. Green ash and the black ash trees are preferred by EAB. White ash is also killed rapidly, but usually only after green and black ash trees are eliminated. Blue ash displays some resistance to the emerald ash borer by forming callous tissue around EAB galleries; however, usually they are also eventually killed. Upon the arrival of EAB in North America, many of the specialized predators and parasitoids that suppressed its populations in Asia were not present in North America. Predators and parasitoids native to North America do not sufficiently suppress EAB, so populations continue to grow and kill nearly 100% of ash trees in an area approximately 10 years after introduction. EAB populations can spread 20 km a year. However, it primarily spreads long-distance by transport of firewood and other wood products that contain ash bark, which allows EAB to spread to new areas to create satellite populations outside of the main infestation and quickly increase its range.
Other factors can limit spread. Climate research suggests that EAB growth may be stemmed in areas too cold for the beetle to survive. North American predators and parasitoids can cause high EAB mortality occasionally, but generally offer limited control. Mortality due to woodpeckers is variable, and parasitism by parasitoids such as Atanycolus cappaerti can be high, but overall parasitism is generally low.
Environmental and economic impacts
EAB threatens the entire North American Fraxinus genus. It has killed at least tens of millions of ash trees so far and threatens to kill most of the 8.7 billion ash trees throughout North America. Emerald ash borer kills young trees several years before reaching their seeding age of 10 years. The loss of ash from an ecosystem can result in increased numbers of invasive plants, changes in soil nutrients, and effects on species that feed on ash.
Damage and efforts to control the spread of EAB have affected businesses that sell ash trees or wood products, property owners, and local or state governments. Quarantines can limit the transport of ash trees and products. Economic impacts are especially high for urban and residential areas due to treatment or removal costs and decreased land value from dying trees. Costs for managing these trees can fall upon homeowners or local municipalities. For municipalities, removing large numbers of dead or infested trees at once is costly, so slowing down the rate at which trees die through removing known infested trees and treating trees with insecticides can allow local governments more time to plan, remove, and replace trees that would eventually die. This strategy saves money as it would cost $10.7 billion in urban areas of 25 states between 2009-2019, while removing and replacing all ash trees in these same areas at once would cost $25 billion. Some urban areas such as Minneapolis, Minnesota, have large amounts of ash with slightly more than 20% of their urban forest as ash.
Monitoring and management
In areas where EAB has not yet been detected, surveys are used to monitor for new infestations. Visual surveys are used to find ash trees displaying symptoms of EAB damage and colored traps attractive to EAB are hung in trees as part of a monitoring program. Sometimes trees are also girdled to act as a trap tree by attracting egg-laying female EAB in the spring and debarking the trees in the fall to search for larvae. If detected, the area is typically placed under a quarantine to prevent infested wood material from causing new infestations. Further control measures are then taken within the area to slow population growth by reducing EAB numbers, preventing them from reaching reproductive maturity and dispersing, and reducing the abundance of ash trees.
Government agencies in both the USA and Canada have utilized a native species of wasp, Cerceris fumipennis, as a means of detecting areas to which EAB has spread. The females of these wasps hunt beetles in the same family as EAB and, therefore, will hunt EAB if it is present. The wasps stun the beetles and carry them back to their burrows in the ground where they are stored until the wasps’ eggs hatch and the wasp larvae feed on the beetles. Volunteers catch the wasps as they return to their burrows carrying the beetles to determine whether any of the catch consists of EAB. If it does, the agencies running the program know that proper quarantine measure must be instituted. This methodology is known as biological surveillance, as opposed to biological control, because it does not appear that the wasps have a significant negative impact on EAB populations.
Tree removal and replacement
In urban areas, trees are often removed once an infestation is found to reduce EAB population densities and the likelihood of further spread. Urban ash are typically replaced with non-ash species such as maple, oak, or linden to limit food sources for EAB. In rural areas, trees can be harvested for lumber or firewood to reduce ash stand density, but quarantines may apply, especially in areas where the material could be infested.
Insecticides are typically only recommended in urban areas or high value trees near an infestation. Insecticides with active ingredients such as imidacloprid, emamectin benzoate, and dinotefuran are currently recommended since they are systemic (i.e., incorporated into the tree) and remain effective for one to three years depending on the product. Ash trees are primarily treated by direct injection into the tree or soil drench. Some insecticides cannot be applied by homeowners and must be applied by licensed applicators. Initially, tree injections will not compromise tree health, but over many years drilling and chemical wounds will compromise the tree's health. Damage from EAB can continue to increase over time even with insecticide applications. Insecticide treatments are not feasible for large forested areas outside of urban areas.
The native range of EAB in Asia was surveyed for parasitoid species that parasitize EAB and do not attack other insect species in the hope they would suppress EAB populations when released in North America. Three species imported from China are currently approved by the USDA for release: Spathius agrili, Tetrastichus planipennisi, and Oobius agrili. All three species have been documented parasitizing EAB larvae one year after release indicating they survived the winter.
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