The emerald ash 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 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 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 .
Life Cycle Stages
Adult: Adults emerge from mid May to early June, depending on local conditions. According to Cappaert “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 and hatch in seven to nine days.
Larva: Studies in southeastern Michigan revealed that larvae hatch in late June or early August . According to Scarr “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.
Pupa: Cappaert 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.
Adults emerge from exit holes in tree trunks from mid-May onwards. In captivity most females lay 60-90 eggs, although up to 258 eggs has been recorded over a 6 week span.Eggs are laid in bark crevices or under bark flaps. Eggs are cream colored, but turn reddish brown after a few days .
What Ecosystem does it Invade and How?
The emerald ash borer (EAB) is an invasive insect that was accidentally introduced from Asia to North America during the early 1990's, although not discovered until 2002 . It can be specially found in China, Japan, Korea and parts of eastern Russia and eastern parts of Canada. As of May 2010, EAB has been detected in 13 states and 2 Canadian provinces. Also they have be transported to United States in wood packing materials made of ash trees. In 2013 the EAB was found in Granville and Warren Counties in North Carolina. The EAB can spread naturally by flying to new host trees upon emergence , but this dispersal is limited to a few miles a year. Lots of beetles are transported by ash wood products by humans.
Ecological Impacts of EAB
Most EAB-induced ash mortality within an invaded stand occurs over just a few years , resulting in relatively synchronous, widespread gap formation with potentially cascading direct and indirect effects on forest community composition and ecosystem processes . These effects include altered understory environment, nutrient cycles, and successional trajectories; facilitation of the spread of light-limited invasive plants; and increased coarse woody debris. Furthermore, at least 282 arthropod species feed on ash, including at least 43 monophagous species native to North America that may be at risk of coextirpation as ash is eliminated from the ecosystem. Given that Fraxinus is one of the most widely distributed tree genera in North America, the ecological impacts of the EAB invasion are likely to be experienced on a continental scale.
Economical and Cultural Effects of EAB
Much of the economic impact of EAB is associated with treatment and/or removal and replacement of high-value trees in urban and residential areas. Ash has been one of the most commonly planted trees in urban and suburban landscapes across the continental United States), comprising more than 20% of the trees in many municipalities across the country. Anroles in storm water capture, reduce levels of airborne pollutants, and provide other ecosystem and asthma, faster recovery from surgery, improved air quality, and increased physical activity, are associated with urban trees.Whereas economic costs associated with EAB can be estimated, cultural impacts are much more difficult to assess and quantify. For several Native American and First Nation tribes in eastern North America, black ash is particularly valued as a spiritual resource. Black ash basketry, an art passed from generation to generation, serves as a means to preserve cultural values as well as a source of income. Basket-making families carefully select and harvest a few black ash trees each year from traditional harvest grounds. Multiple generations come together to debark and pound the logs with sledgehammers until the growth rings separate, producing long strips of wood that can be woven into baskets. Baskets of all shapes and sizes are produced. Some are destined for practical everyday use, and others are striking works of art. Cooperative efforts to collect and preserve ash seeds, including seeds from black ash trees, have been undertaken by a number of tribes and scientists from federal and state agencies and universities.
Early Eracdiction Efforts
Beginning in 2003, USDA APHIS, in cooperation with other federal and state agencies, developed a plan that called for containing the known EAB infestations in southeast Michigan and Windsor, Ontario, while eradicating localized, satellite populations, termed outliers . There was no practical way to reduce EAB populations on a large scale with insecticides, particularly given the size of the infestations. It was theorized that if the rate of EAB expansion could be significantly slowed, the high ash mortality in the core would reduce EAB carrying capacity, collapsing the EAB population and potentially providing opportunities to drive population densities below the Allee threshold and thus to extinction . Quarantines to limit the risk of new EAB introductions were imposed to regulate transport of ash trees, logs, firewood, and related items out of infested areas. The goal of eradicating EAB was eventually abandoned as additional outlier infestations were discovered in more states and funding became limited.
Insecticide trials conducted in the first few years following the discovery of EAB in North America generated inconsistent results. In some cases, systemic insecticides adequately protected trees from EAB, but the same treatments failed or produced mixed results in other trials . Some studies conducted over multiple years revealed that EAB damage continued to increase despite ongoing treatment. Systemic insecticides to control EAB include products (a) applied as soil injections or drenches, (b) injected into the base of the trunk, or (c) sprayed on the basal 1.5 m of the trunk . One product with the active ingredient emamectin benzoate has provided up to three years of nearly 100% EAB control in some trials . These advances have dramatically increased the likelihood that ash trees can be protected successfully throughout the EAB invasion wave.Moreover, analyses have shown that costs of protecting trees are substantially lower than costs of removal, especially when the value of ecosystem services provided by trees, such as storm water capture, is considered.