Emerald ash borer

The emerald ash borer (Agrilus planipennis) is a green buprestid or jewel beetle native to north-eastern Asia that feeds on ash species. 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. Prior to being 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, insecticides, and biological control. The French priest and naturalist Armand David collected a specimen of the species 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 the first brief description of Agrilus planipennis by the entomologist Léon Fairmaire was published in the Revue d'Entomologie in 1888. Unaware of Fairmaire's description, a separate description naming the species as Agrilus marcopoli was published in 1930 by Jan Obenberger. Adult beetles are typically bright metallic green and about 8.5 millimeters (0.33 in) long and 1.6 millimeters (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. Adults beetles of other species can often be misidentified by the public. 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. 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 1000 degree-days. After emergence, adults feed for one week on ash leaves in the canopy before mating, but cause little defoliation in the process. 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. 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 (0.02 to 0.04 in) in diameter, and are initially white, but later turn reddish-brown if fertile. After hatching, larvae chew through the bark to the inner phloem, cambium, and outer xylem 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 about 1.25 centimeters (0.49 in) into 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 overwintering again and emerging as adults the following spring. This two-year life cycle is more common in cool climates, such as European Russia. The native range of the emerald ash borer is temperate north-eastern Asia, which includes Russia, Mongolia, northern China, Japan, and Korea. 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 Massachusetts. In eastern Europe, a population was found in Moscow, Russia, in 2003. From 2003 to 2016, this population has spread west towards the European Union at up to c. 40 km (25 mi) per year and is expected to reach central Europe between 2031 and 2036. Although not recorded from the European Union as of 2019, it has already spread to far eastern Ukraine from neighboring Russia.