Agrilus planipennis

Geographic Range

Emerald ash borers are beetles native to northeastern China, Japan, Korea and Russia that are an invasive species in North America. They were first discovered in the United States in 2002 in Michigan, and have since spread to Ohio, Indiana, Illinois, and Maryland, as well as several surrounding states. Emerald ash borers have also been found in Ontario, Canada. Emerald ash borers are only capable of naturally dispersing themselves an average of 1.1 km per year. Their major cause of dispersal is human transportation.

• Biogeographic Regions
• nearctic nearctic
  • introduced introduced
• palearctic palearctic
  • native native

Habitat

Emerald ash borers rely on ash trees to complete their life cycle. Adult female beetles lay their eggs on the bark of ash trees and when these eggs hatch, the larvae chew their way through the bark layer into the cambium layer. The larvae of emerald ash borers remain in the cambial layer until they are ready to emerge from the tree as adult beetles.

Ash trees are commonly used as both ornamental trees in urban settings and as wind breakers in agricultural settings to protect crops. Adult beetles use the ash foliage as their source of food and use the leaf or trunk surfaces of the ash tree for mating.

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest

• Other Habitat Features
• urban urban
• suburban suburban
• agricultural agricultural

Physical Description

Emerald ash borers as adults are elongate, cylindrical, slender beetles that can grow to be approximately 7.5 to 15 mm long and 3 mm wide. As adults, emerald ash borers can be recognized by a metallic green sheen with a coppery-red abdomen that is hidden under the wings. Males are densely covered with setae on their thorax, whereas the setae are more sparsely spread on the females. Females appear to have larger bodies than males.

Adult females lay eggs that are 1 mm in diameter on the bark of ash trees. Eggs are white when laid, and turn amber as they develop. Eggs hatch into flattened, segmented larvae that chew their way through the bark and tunnel into the tree's inner cambial layer. Larvae can reach 23 to 26 mm in length and have a pincer-like appendage called a urogomphi attached to the last abdominal segment.

• Other Physical Features
• heterothermic heterothermic

• Sexual Dimorphism
• female larger

Development

Adult females lay eggs that are 1 mm in diameter on the bark of ash trees. Eggs are white when laid, and turn amber as they develop. The eggs hatch within 15 days into their flattened, segmented larval state. Larvae chew their way through the bark and tunnel into the tree's inner cambial layer. By tunneling through the phloem, they disrupt the tree's transportation of nutrients. The larval stage is the longest within the life cycle, lasting about 300 days. This generally occurs between June to April of the next year. Emerald ash borers have four larval stages. In late summer and early fall, larvae in their final stage enter the layers of bark and prepare a chamber where they remain during the winter months as prepupae. Larvae can reach 23 to 26 mm in length. The larvae have a pincer-like appendage called a urogomphi attached to the last abdominal segment.

The overwintering physiology of the emerald ash borer prepupae allows them to accumulate glycerol in high concentrations along with other antifreeze agents. This behavior contributes to the emerald ash borer's ability to tolerate cold temperatures. The larvae complete development within their pupation chambers in the summer.

After maturing into adults within their chambers, fully developed adults chew their way out from their chamber within the bark. This process generally occurs on days with high temperatures and begins in mid-May, with adult activity peaking in June and July. D-shaped holes within the bark can be observed from the outside of an infested ash tree where a fully developed beetle has emerged. After they emerge, fully developed beetles are capable of flying.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

Males generally emerge before the females. After emerging, both males and females mature for 5 to 7 days before they can begin to mate. During this period of maturation, emerald ash borers feed on foliage. Males locate females using sex pheromones and visual cues. After mates are chosen, emerald ash borers mate on a host tree for about fifty minutes. Males do not guard their mates. Both male and female emerald ash borers have multiple mates.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Once a male has located a female to mate with, the male drops out of the air onto the female. Females receive a spermatophore from the males. It is suggested that since the transfer of spermatophores is not always successful, having multiple mates is necessary to ensure fertilization and leads to the emerald ash borers successful establishment and spread.

After finding a mate, females begin to lay their eggs anywhere from 7 to 10 days after mating, and continue laying eggs for 4 to 6 weeks. Females have a long ovipositor that is used to place eggs within the cracks of bark. On average, they lay 70 eggs during a few weeks. However, the number of eggs laid can be anywhere from 50 to 200. Females place eggs individually, and they hatch within 2 weeks after laying.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

There is no information suggesting parental care or investment after birth. However, it is suggested that females consider the location of where they are laying their eggs. Adult females take great care into finding bark crevices that are difficult to find and are not easily exposed to bad weather.

• Parental Investment
• female parental care female parental care
• pre-fertilization
  • provisioning

Lifespan/Longevity

The larval stage of emerald ash borers is the longest phase in the life cycle, lasting approximately 300 days. After emerging from the host tree, adult emerald ash borers live for 3 to 6 weeks. During this period, both males and females continue to feed and mate.

Behavior

Emerald ash borers are not social and therefore do not show evidence of forming any social hierarchies. They are capable of flying up to 2.8 km per day at a speed of 3 mph. Females that have already mated fly twice as far as those that have not. This suggests that mated females fly longer distances to find new host ash trees to lay their eggs on. The maximum distance flown by an emerald ash borer is about 10 km.

• Key Behaviors
• arboreal arboreal
• flies
• parasite parasite
• motile motile
• sedentary sedentary
• solitary solitary

Home Range

Emerald ash borers are capable of flying 5.2 km in 40 hours. If there is an ash tree nearby, they are more likely to fly less than 100 km. It is estimated that ash trees within a 0.5 mile radius of a known infected tree can also be infested with emerald ash borer larvae.

Communication and Perception

Emerald ash borers are known to communicate using visual and chemical cues. Evidence for interaction based on visual cues comes from attempts to develop an emerald ash borer traps, where adult beetles were attracted to purple paneled traps. Emerald ash borers also have a series of chemoreceptors used to perceive their environment using taste and smell. Emerald ash borers use sensilla as their sense organs. Sensilla are present on the antennae used for smell and also on the mouth and legs used for taste. Since males tend to have more taste sensilla than females, it is suggested that short range contact cues are used for mate recognition. Other species of beetles also have a tympanic membrane backed by a tracheal airsac, which suggests that beetles are capable of responding to auditory cues as well.

• Communication Channels
• visual visual
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• acoustic acoustic
• chemical chemical

Food Habits

Emerald ash borers are folivores in the adult phase, and lignivores in the larval phase. As adults, emerald ash borers feed upon the leaves of ash trees, leaving behind noticeable ridges along the leaf edge. Upon hatching on the bark, larvae chew their way inward and feed upon the phloem and cambial region of the tree. This action prevents nutrients from photosynthesis from being transported and eventually leads to the tree's death.

• Primary Diet
• herbivore herbivore
  • folivore folivore
  • lignivore

• Plant Foods
• leaves
• wood, bark, or stems

Predation

A variety of woodpecker species are found in the emerald ash borer's native geographical range in China are known to prey upon emerald ash borer larvae. Woodpeckers use visual cues, such as damaged trees with holes in the bark, vibrations, and other systematic foraging behaviors to locate the larvae. Predators include great spotted woodpeckers ( Dendrocopos major ) and grey-headed woodpeckers ( Picus canus ).

Ecosystem Roles

Emerald ash borer larvae feed on the phloem and cambrium layers as well as the shallow sapwood under the bark. This slowly starves the tree of essential nutrients, deeming it unable to support itself with essential nutrients. Once the larvae hatch and bore into the cambium layer, they feed in a very distinguishable zigzag pattern up and down the trunk. By disrupting the transportation of nutrients, an infested tree often dies within 2 to 3 years.

One species of wasp ( Oobius agrili ) is an egg parasitoid of emerald ash borers, while two others ( Spathius agrili and Tetrastichus planipennisi ) are larval parasitoids. Some of these species are being introduced to the United States in an attempt to control emerald ash borer outbreaks.

• Ecosystem Impact
• parasite parasite

Economic Importance for Humans: Positive

Emerald ash borers have no known positive impacts on humans.

Economic Importance for Humans: Negative

Emerald ash borers are extremely invasive beetles responsible for killing over 15 million ash trees in the state of Michigan, where the initial North American invasion occurred. The detection of an emerald ash borer invasion is extremely difficult, due to the fact that by the time an ash tree begins to show signs of being stressed, it is too late. The net impact of emerald ash borers on United States industries such as agriculture, forestry, fisheries is roughly $134 million annually. In all, it is estimated that it would cost $1 million dollars a year for the removal and replacement of infested trees.

The treatment and removal of infested ash trees is hugely expensive and time-consuming. Several costly experiments have been performed with no definitive solution to stopping the spread of the emerald ash borer. One such experiment involved an eradication protocol that called for the removal of every ash tree within a 0.8 km radius of an infected tree. It is estimated that this process of attempting to eradicate emerald ash borers cost upwards of $100 million. However, this experiment had other detrimental consequences, in that researchers unintentionally caused a secondary spread of invasive plant species to inhabit areas where the trees had been removed. This was due to the increased sunlight and space available where the trees once stood.

Other attempts to prevent their transportation include several quarantines on the transport of wood from infested areas. This quarantine involves mandatory inspections of wood crossing the Mackinac Bridge in Michigan, which seeks to prevent their spread into the Upper Peninsula. Quarantines can be particularly hard on the timber industry. In addition to quarantines, education and outreach programs are important for the prevention of further outbreaks.

• Negative Impacts
• crop pest

Conservation Status

Emerald ash borers are not endangered.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Ashley Fooy (author), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.

References

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