Taxonomic name: Agrilus planipennis Fairmaire
Common names: emerald ash borer
Organism type: insect
Agrilus planipennis, commonly known as the emerald ash borer (EAB), is an insect from a family of beetles generally referred to as metallic wood-boring beetles. A. planipennis is native to Asia and eastern Russia, and is only a minor pest in its native range. The beetle was discovered in Michigan and Ontario, Canada in 2002. Despite quarantine regulations and eradication attempts including burning of large numbers of infested trees, A. planipennis continues to spread. It is now present in Illinois, Indiana, Maryland, Michigan, Missouri, Ohio, Pennsylvania, Virginia, Wisconsin, West Virginia and parts of Canada. It colonizes and kills ash trees in the genus Fraxinus killing healthy ash trees in urban and forested areas. It now threatens more than eight billion ash trees in the continental United States. This has had significant ecological and economic effects. Similar damage is now occurring in the region of Moscow, Russia which causes serious concern for Europe if it continues to spread.
The adult A. planipennis is 8.5 - 14.0 mm long and 3.1 - 3.4 mm. wide. The body which is narrow, elongate and cuniform is a metallic blue-green colour. It is commonly called the emerald ash borer. Mature larvae are 26 - 32 mm long and creamy white in color. The head of the larva is flat and the vertex is shield-shaped. The compound eyes are kidney shaped and somewhat bronze coloured. The prothorax is transversely rectangular and it is slightly wider than the head, but is the same width as the anterior margin of the elytra. The anterior margin of the elytra is raised forming a transverse ridge, the surface of which is covered with punctures. The posterior margins of the elytra are round and obtuse with small tooth-like knobby projections on the edge. The eggs of the emerald ash borer which are light yellow in colour turn brownish yellow just before hatching. The eggs which have a slightly convex centre are oval and 1 x 0.6 mm in size. The head is small and brown and it is retracted into the prothorax, exposing only the mouthparts. The prothorax is enlarged, whereas the meso- and meta-thorax are slightly narrower; the mesothorax bears spiracles. The abdomen is 10-segmented; the 1st to 8th segments with one pair of spiracles each and the last segment bears one pair of brownish serrated styles. Pupae are 10 -14 mm long and they are creamy white in color. The antennae stretch back to the base of the elytra and the last few segments of the abdomen bend slightly ventral (Nomura, 2002).
Agrilus anxius, Agrilus bilineatus, Agrilus subcinctus
agricultural areas, natural forests, planted forests, urban areas
Nomura (2002) states that, "During the early stage of an infestation, when A. planipennis population is low, the initial damage is low. However, after 2 to 3 years of continuous infestation, the population builds up, and eventually the tree's nutrient and water transport system is disrupted, culminating in wilting and eventual tree mortality. A. planipennis will kill apparently healthy trees during high beetle population levels which are probably triggered by a few years of hot and dry climatic conditions. A. planipennis can cause severe damage to ash stands over 8 years of age that are not crown-closed, with good sun light penetration, and that are comprised of trees with bark fractures. After 1 to 2 years of infestation, the bark often falls off in pieces from damaged trees thereby exposing the tunnel-ridden sapwood."
Nomura (2002) reports that damage consists of, "D-shaped exit holes along the lower bole surface are clear signs of buprestid beetle activity, however, careful examination is required as these are very cryptic. Frass filled, zigzagging tunnels about 6mm wide at the sapwood/bast interface are signs of A. planipennis feeding. Callus tissue produced by the tree in response to larval feeding may cause vertical splits 5 -10cm in length to occur in the bark above a gallery." MDNR (2004) states that, "Infested trees exhibit top-down dieback, with 1/3 to 1/2 of branches dying the first year and the remaining canopy dying the following year. This is often followed by a large number of shoots arising below the dead portions of the trunk. Borers make a small (1/16 inch diameter) "D"-shaped hole when entering the tree and several distinct "S"-shaped tunnels may be present under the bark. Trees may also exhibit 5-10cm vertical splits in the bark in response to larval feeding.
A. planipennis attacks ash trees in the genus Fraxinus. All North American ash species that occur within the current EAB range have been killed by EAB, including white ash (F. Americana), green ash (F. pennsylvanica), black ash (F. nigra), blue ash (F. quadrangulara) and pumpkin ash (F. profunda) (Lindell et al. 2008). Attacks on non-ash species have not been observed in North America to date, but there is concern that other species could be vulnerable. If A. planipennis host range extends beyond Fraxinus spp., the impacts of this invasive pest in North American forests would increase dramatically. Anulewicz et al. (2008) assessed A. planipennis landing rates, oviposition and larval development in a number of North American tree species. They found that “although A. planipennis adults will occasionally land on and oviposit on logs and trees of non-ash species, A. planipennis larvae did not successfully develop on anything other than Fraxinus species” (Anulewicz et al. 2008).
The three main ash species in Europe are F. excelsior, the most widespread species, and F. ornus and F. angustifolia. Nothing is known of the susceptibility of these to A. planipennis, so evaluating the resistance of these European species should be a research priority. F. excelsior is a common forest and urban tree used for timber, flooring, tool making and for its medicinal properties (FRAXIGEN 2005 in Baranchikov et al. 2008). All three species are important components of forest ecosystems in Europe and “their disappearance would have serious consequences for native biodiversity and ecosystem services” (Baranchikov et al. 2008).
Native range: The emerald ash borer’s native range includes China, Mongolia, North Korea, South Korea, Japan, Taiwan, and the Russian Far East (APHIS-USDA 2008).
Known introduced range: In North America, EAB infestations are known to exist in Illinois, Indiana, Maryland, Michigan, Missouri, Ohio, Pennsylvania, Virginia, Wisconsin and West Virginia, as well as the Canadian provinces of Ontario and Quebec (APHIS-USDA 2008). It has also recently been discovered in the Moscow region of Russia (Baranchikov et al 2008).
Introduction pathways to new locations
Forestry: Although Agrilus planipennis is a good flier, human activities are the primary cause of long distance spread. This includes moving infested trees, logs, and firewood (MDNR, 2004).
Nursery trade: Movement of infected nursery stock (Herms et al. 2003).
Transportation of habitat material: Nomura (2002) states that, "Any life stage (eggs, larvae, pupae and adults) can be moved with raw wood with bark for processing, dunnage and crating for heavy goods, nursery stock, lumber and wood with bark attached and firewood, etc."
Local dispersal methods
Natural dispersal (local): Nomura (2002) states that, "Flight dispersal is generally reported to be local, usually not more than 8 to 12 m in distance and not more than 1 to 2 m in height. However, according to Nomura, this particular species differs from other members of the genus and is capable of dispersal flight up to a few kilometres to seek new host material."
Adults emerge from exit holes in tree trunks from mid-May onwards. Mating occurs seven to ten days after emergence and multiple matings often occur (Bauer et al. 2004a; Lyons et al. 2004 in Cappaert et al. 2005).Oviposition occurs seven to nine days after mating (Nomura 2002) .In captivity most females lay 60-90 eggs, although up to 258 eggs has been recorded over a 6 week span (Lyons et al. 2004 in Cappaert et al. 2005). Eggs are laid in bark crevices or under bark flaps. Eggs are cream colored, but turn reddish brown after a few days (Bauer et al. 2004a in Cappaert et al. 2005).
Initial observations led researchers to believe that A. planipennis had a one year life cycle in North America and other introduced locations (e.g. Scarr et al. 2002). However further observations caused Cappaert et al. (2005) to reevaulate the voltinism of A. planipennis and suggest that it actually has a semivoltine (two year) life cycle in North America. “It is not yet clear why delayed larval development occurs or what proportion of A. planipennis larvae require 2 yr for development. Although delayed development appears to be more common in low-density A. planipennis populations, we also have found that 2-yr development occurs occasionally in moderately to heavily infested trees in the core area of the infestation. It is possible that a second year of development is required when oviposition occurs late in the summer and larvae do not reach the prepupal stage before winter. Alternatively, a chemical or mechanical defensive response by newly infested trees may slow larval development, but other factors, such as cold temperatures or low nutrient levels, may also be involved. Additional studies are planned to address this phenomenon because it has important implications for survey activities and dynamics of A. planipennis population” (Cappaert et al. 2005).
Adult: Adults emerge from mid May to early June, depending on local conditions. According to Cappaert et al. (2005) “Adults live for around 3 to 6 weeks, with peak activity from late June to early July in southeastern Michigan. Adults feed on ash foliage for 5 to 7 days before mating, and females feed for another 5 to 7 days before oviposition.”
Egg: Eggs are laid in bark crevices or under bark flaps (Bauer et al. 2004a in Cappaert et al. 2005) and hatch in seven to nine days (Nomura 2002).
Larva: Studies in southeastern Michigan revealed that larvae hatch in late June or early August (Cappaert et al. 2005). According to Scarr et al. (2002) “After hatching, first-instar larvae initially bore through the bark to feed on the phloem and eventually feed on the outer surface of the sapwood as they grow. Growing larvae as they feed form tunnels that are flat and wide, and zig-zag (S-shaped) throughout the bast and outer sapwood. Tunnels may be as long as 9 to16 cm and they are filled with brownish sawdust and frass. In Michigan, U.S.A. tunnels are reported to be between 20 and 30 cm long. Most of the tunnels tend to occur in the basal portion of the tree trunk up to a height of 1.8 m.” Cappaert et al. (2005) report that “As larvae feed they excise serpentine galleries through phloem, until cessation of feeding in October or November. Larvae then excavate a ~1cm deep cell in the sapwood or outer bark where they overwinter as prepupal larvae. Larvae pass through four instars”.
Pupa: Cappaert et al. (2005) report that “Pupation begins in mid-April and continues into May. Adults emerge approximately 3 weeks later.” Pupal development is variable according to humidity and temperature. After pupae transform into adults in the spring, the beetle takes 1 to 2 weeks before it emerges through D-shaped exit holes 3-4 mm wide (APHIS-USDA 2008).
Reviewed by: Dr. Deborah G. McCullough Associate Professor Dept. of Entomology and Dept. of Forestry Michigan State University USA
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Monday, 14 August 2006