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.
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.
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)
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).
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)
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.
The emerald ash borer (Agrilus planipennis), also known by the acronym EAB, is a green buprestid or jewel beetle native to north-eastern Asia that feeds on ash species (Fraxinus spp.). Females lay eggs in bark crevices on ash trees, and larvae feed underneath the bark of ash trees to emerge as adults in one to two years. In its native range, 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. Before it was found in North America, very little was known about emerald ash borer in its native range; this has resulted in much of the research on its biology being focused in North America. Local governments in North America are attempting to control it by monitoring its spread, diversifying tree species, and through the use of insecticides and biological control.
French priest and naturalist Armand David collected a specimen of the species during one of his trips through Imperial China in the 1860s and 1870s. He found the beetle in Beijing and sent it to France, where the first brief description of Agrilus planipennis by the entomologist Léon Fairmaire was published in the Revue d'Entomologie in 1888.[2] Unaware of Fairmaire's description, a separate description naming the species as Agrilus marcopoli was published in 1930 by Jan Obenberger.[2]
Adult beetles are typically bright metallic green and about 8.5 mm (0.33 in) long and 1.6 mm (0.063 in) wide. Elytra are typically a darker green, but can also have copper hues. Emerald ash borer is the only North American species of Agrilus with a bright red upper abdomen when viewed with the wings and elytra spread. The species also has a small spine found at the tip of the abdomen and serrate antennae that begin at the fourth antennal segment.[3] They leave tracks in the trees they damage below the bark that are sometimes visible.[4] Adult beetles of other species can often be misidentified by the public.[5][6]
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.[7]
After 400–500 accumulated degree-days above 10 °C (50 °F), adults begin to emerge from trees in late spring, and peak emergence occurs around 1,000 degree-days. After emergence, adults feed for one week on ash leaves in the canopy before mating, but cause little defoliation in the process.[8] Males hover around trees, locate females by visual cues, and drop directly onto the female to mate. Mating can last 50 minutes, and females may mate with multiple males over their lifespan.[9] 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.[8]
Eggs are deposited between bark crevices, flakes, or cracks and hatch about two weeks later. Eggs are approximately 0.6 to 1.0 mm (0.02 to 0.04 in) in diameter, and are initially white, but later turn reddish-brown if fertile.[8][7] After hatching, larvae chew through the bark to the inner phloem, cambium, and outer xylem where they feed and develop.[9] Emerald ash borer has four larval instars. By feeding, larvae create long serpentine galleries. Fully mature fourth-instar larvae are 26 to 32 mm (1.0 to 1.3 in) long.[7] In fall, mature fourth-instars excavate chambers about 1.25 cm (0.49 in) into the sapwood or outer bark where they fold into a J-shape.[9] 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 overwintering again and emerging as adults the following spring.[7] This two-year life cycle is more common in cool climates, such as European Russia.[10]
Larva
Pupa removed from its pupal chamber.
Adults exit the tree from D-shaped holes.
Dorsal view of adult with elytra and wings spread.
Underside of an adult emerald ash borer.
The native range of the emerald ash borer is temperate north-eastern Asia, which includes Russia, Mongolia, northern China, Japan, and Korea.[11][10]
The beetle is invasive in North America where it 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,[12][13] and in the Pacific Northwest in Oregon.[14][15][16] In eastern Europe, a population was found in Moscow in 2003.[10] 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.[17][18][10] Although not recorded from the European Union as of 2019, it has already spread to far eastern Ukraine from neighboring Russia.[19][20][21][22]
In its native range, emerald ash borer is only a nuisance pest on native trees, as population densities typically do not reach levels lethal to healthy trees.[23] In China, it infests native Fraxinus chinensis, F. mandshurica, and F. rhynchophylla; in Japan it also infests F. japonica and F. lanuginosa.[10]
Emerald ash borer primarily infest and can cause significant damage to ash species including green ash (F. pennsylvanica), black ash (F. nigra), white ash (F. americana), and blue ash (F. quadrangulata) in North America.[24] In Europe, F. excelsior is the main ash species colonized, which is moderately resistant to emerald ash borer infestation.[10][25] Ash susceptibility can vary depending on the attractiveness of chemical volatiles to adults, or the ability of larvae to detoxify phenolic compounds.[9] Emerald ash borer has also been found infesting white fringe tree in North America, which is a non-ash host, but it is unclear whether the trees were healthy when first infested, or were already in decline because of drought.[9][26] Another non-ash host has also been discovered, Olea europaea, albeit in a lab setting.[27]
Adults prefer to lay eggs on open grown or stressed ash but readily lay eggs on healthy trees amongst other tree species. Ashes that grow in pure stands, whether naturally occurring or in landscaping, are more prone to attack than isolated trees or ones located in mixed forest stands. Ashes used in landscaping also tend to be subjected to higher amounts of environmental stresses including compacted soil, lack of moisture, heating effects from urban islands, road salt, and pollution, which may also reduce their resistance to the borer. Furthermore, most ashes used in landscaping were produced from a handful of cultivars, resulting in low genetic diversity.[9] Young trees with bark between 1.5 mm (0.059 in) to 5 mm (0.20 in) are preferred.[10] Both males and females use leaf volatiles and sesquiterpenes in the bark to locate hosts.[9] Damage occurs in infested trees by larval feeding. The serpentine feeding galleries of the larvae disrupt the flow of nutrients and water, effectively girdling, thus killing the tree, as it is no longer able to transport sufficient water and nutrients to the leaves to survive. Girdled ashes will often attempt to regenerate through stump sprouting, and there is evidence that stressed trees may also generate higher than normal seed crops as an emergency measure.[8]
Outside its native range, emerald ash borer is an invasive species that is highly destructive to ash trees in its introduced range.[28] Before emerald ash borer was found in North America, very little was known about the insect in its native range aside from a short description of life-history traits and taxonomic descriptions, which resulted in focused research on its biology in North America.[8] The insect was first identified in Canton, Michigan (near Detroit[29]), in 2002,[29] but it may have been in the U.S. since the late 1980s.[30] It is suspected that it was introduced from overseas in shipping materials such as packing crates.[29]
Without factors that would normally suppress emerald ash borer populations in its native range (e.g., resistant trees, predators, and parasitoid wasps), populations can quickly rise to damaging levels.[8] After initial infestation, all ash trees are expected to die in an area within 10 years without control measures.[8] Every North American ash species has susceptibility to emerald ash borer, as North American species planted in China also have high mortality from infestations, but some Asian ash species are resistant, including F. baroniana, F. chinensis, F. floribunda, F. mandshurica, and F. platypoda.[31][32][33]
Green ash and black ash trees are preferred by emerald ash borer. White ash is also killed rapidly but usually only after all green and black ash trees are eliminated. Blue ash is known to exhibit a higher degree of resistance to emerald ash borer, which is believed to be caused by the high tannin content in the leaves making the foliage unpalatable to the insect. While most Asian ashes have evolved this defense, it is absent from American species other than blue ash. Researchers have examined populations of so-called "lingering ash", trees that survived ash borer attack with little or no damage, as a means of grafting or breeding new, resistant stock. Many of these lingering ashes were found to have unusual phenotypes that may result in increased resistance. Aside from their higher tannin content, Asian ashes also 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.[34] Many of the specialized predators and parasitoids that suppressed emerald ash borer in Asia were not present in North America. Predators and parasitoids native to North America do not sufficiently suppress emerald ash borer, so populations continue to grow. Birds such as woodpeckers feed on emerald ash borer larva, although the adult beetles have not been used by any American fauna as food.[8] Emerald ash borer populations can spread between 2.5 to 20 km (1.6 to 12.4 mi) per year.[8] It primarily spreads through flight or by transportation of ash bark containing products such as firewood or nursery stock, which allows it to reach new areas and create satellite populations outside of the main infestation.[8][10]
Other factors can limit spread. Winter temperatures of approximately −38 °C (−36 °F) limit range expansion.,[35][36] and overwintering emerald ash borer survive down to average temperatures of −30 °C (−22 °F) because of antifreeze chemicals in the body and insulation provided by tree bark.[10] Larvae can also survive high heat up to 53 °C (127 °F). Conversely, much like ashes grown in the nursery trade, the population of emerald ash borer in North America is believed to have originated from a single group of insects from central China and also exhibits low genetic diversity.[10]
North American predators and parasitoids can occasionally cause high emerald ash borer mortality, but generally offer only limited control. Mortality from native woodpeckers is variable. Parasitism by parasitoids such as Atanycolus cappaerti can be high, but overall such control is generally low.[8]
The United States Department of Agriculture's Animal and Plant Health Inspection Service published a rule on December 14, 2020—to take effect one month later, January 14, 2021—ending all EAB quarantine activities in the United States due to ineffectiveness so far.[37][38] Other means will be used instead, especially biological controls (see §Biological control below).[37][38]
Emerald ash borer threatens the entire North American genus Fraxinus. It has killed tens of millions of ash trees so far and threatens to kill most of the 8.7 billion ash trees throughout North America.[12] Emerald ash borer kills young 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 can result in increased numbers of invasive plants, changes in soil nutrients, and effects on species that feed on ash.[10]
Damage and efforts to control the spread of emerald ash borer have affected businesses that sell ash trees or wood products, property owners, and local or state governments.[8] Quarantines can limit the transport of ash trees and products, but economic impacts are especially high for urban and residential areas because of treatment or removal costs and decreased land value from dying trees.[39] 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 over 10 years, while removing and replacing all ash trees in these same areas at once would cost $25 billion[39][40] (with another estimate putting the removal alone at $20–60 billion).[29] Some urban areas such as Minneapolis have large amounts of ash with slightly more than 20% of their urban forest as ash.[41]
In areas where emerald ash borer has not yet been detected, surveys are used to monitor for new infestations. Visual surveys are used to find ash trees displaying emerald ash borer damage, and traps with colors attractive to emerald ash borer, such as purple or green, are hung in trees as part of a monitoring program.[8] These traps can also have volatile pheromones applied to them that attract primarily males.[9]
Sometimes trees are girdled to act as trap trees to monitor for emerald ash borer. The stressed tree attracts egg-laying females in the spring, and trees can be debarked in the fall to search for larvae.[8] If detected, an area is often placed under a quarantine to prevent infested wood material from causing new infestations.[30][8] Further control measures are then taken within the area to slow population growth by reducing beetle numbers, preventing them from reaching reproductive maturity and dispersing, and reducing the abundance of ash trees.[8]
Government agencies in both the U.S. and Canada have utilized a native species of parasitoid wasp, Cerceris fumipennis, as a means of detecting areas to which emerald ash borer has spread. The females of these wasps hunt other jewel beetles and emerald ash borer 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 emerald ash borer is present. 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 emerald ash borer populations.[42]
In areas where emerald ash borer is non-native and invasive, quarantines, infested tree removal, insecticides, and biological control are used to reduce damage to ash trees.
Once an infestation is detected, quarantines are typically imposed by state, or previously, national government agencies disallowing transport of ash firewood or live plants outside of these areas without permits indicating the material has been inspected or treated (i.e., heat treatment or wood chipping) to ensure no live emerald ash borer are present in the bark and phloem.[30][43] In urban areas, trees are often removed once an infestation is found to reduce emerald ash borer 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.[44] In rural areas, trees can be harvested for lumber or firewood to reduce ash stand density, but quarantines may apply for this material, especially in areas where the material could be infested.[45]
Kentucky Extension specialists suggest selecting uncommon species to replace removed ashes in the landscape.[46] Previous generations created monocultures by planting ash trees in an overabundance, a factor in the extent of the devastation caused by the emerald ash borer. Favoring instead a diversity in species helps keep urban forests healthy. University of Kentucky scientists suggest choosing monotypic species such as the pawpaw, yellowwood, Franklin tree, Kentucky coffeetree, Osage orange, sourwood, and bald cypress.
Insecticides with active ingredients such as azadirachtin, imidacloprid, emamectin benzoate, and dinotefuran are currently used. Dinotefuran and imidacloprid are systemic (i.e., incorporated into the tree) and remain effective for one to three years depending on the product.[8][47][48] Insecticides are typically only considered a viable option in urban areas with high value trees near an infestation.[47] 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. Damage from emerald ash borer can continue to increase over time even with insecticide applications.[8] Insecticide treatments are not feasible for large forested areas outside of urban areas.[8]
The native range of emerald ash borer in Asia was surveyed for parasitoid species that parasitize emerald ash borer and do not attack other insect species in the hope they would suppress populations when released in North America.[49] Three species imported from China were approved for release by the USDA in 2007 and in Canada in 2013: Spathius agrili, Tetrastichus planipennisi, and Oobius agrili, while Spathius galinae was approved for release in 2015.[50][51] Excluding Spathius galinae, which has only recently been released, the other three species have been documented parasitizing emerald ash borer larvae one year after release, indicating that they survived the winter, but establishment varied among species and locations.[51] Tetrastichus planipennisi and Oobius agrili established and have had increasing populations in Michigan since 2008; Spathius agrili has had lower establishment success in North America, which could be caused by a lack of available emerald ash borer larvae at the time of adult emergence in spring, limited cold tolerance, and better suitability to regions of North America below the 40th parallel.[51]
The USDA is also assessing the application of Beauveria bassiana, an insect fungal pathogen, for controlling emerald ash borer in conjunction with parasitoid wasps.[52]
The emerald ash borer (Agrilus planipennis), also known by the acronym EAB, is a green buprestid or jewel beetle native to north-eastern Asia that feeds on ash species (Fraxinus spp.). Females lay eggs in bark crevices on ash trees, and larvae feed underneath the bark of ash trees to emerge as adults in one to two years. In its native range, 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. Before it was found in North America, very little was known about emerald ash borer in its native range; this has resulted in much of the research on its biology being focused in North America. Local governments in North America are attempting to control it by monitoring its spread, diversifying tree species, and through the use of insecticides and biological control.
