In a study published in Environmental Entomology, the emerald ash borer completes its life cycle in North Carolina in one year instead of the sometimes two-year life cycle found in northern areas of the United States.
According to the researchers, the findings will help them know when to release parasitoid wasps, a key strategy experts have tried to use to control the insect.
This pest originated in Michigan and spread from there, so most of what we know about it in the United States comes from a cooler climate, according to the study’s lead author Ryan Bohannon, a graduate student at North Carolina State University.
Life cycle of invasive insects could aid management in the Southeast
(Photo: Stephen Hocking/Unsplash)
The emerald ash borer, also known as Agrilus planipennis, was discovered in the United States in 2002.
It’s now legal in 36 US states and five Canadian provinces, according to ScienceDaily.
According to Kelly Oten, assistant professor and consulting specialist in forestry and environmental resources at NC State, the insect has been documented in more than 60 of the state’s 100 counties.
The emerald ash borer feeds on all species of ash trees native to the United States, including the white ash, green ash, Carolina ash, and North Carolina pumpkin ash.
Adult beetles lay their eggs on the bark of trees, and the larvae burrow into the tree and feed on the tissues within.
Researchers have attempted to release tiny wasps, some as small as a mosquito, to attack and feed on the emerald ash borer in its natural habitat.
However, Oten claims that the wasps have yet to establish themselves in the warm, southern climate.
The timing of the emerald ash borer’s life cycle could be crucial.
Researchers in central North Carolina collected specimens of the emerald ash borer from under the bark of infested ash trees, brought them back to the lab, and measured them to determine their life stage.
This was done every two weeks for 26 months.
They also captured adult insects to learn more about when they are actively flying and laying eggs.
Researchers are also investigating whether regrowing infested trees can prolong the life of the trees while giving wasps more time to establish themselves.
They also looked for trees with natural genetic resistance to the pest.
Also read: The Emerald Ash Borer is “winning” along the East Coast
Damaged by Emerald Ash Borer
While EAB adults feed on foliage, the damage is insignificant.
Larval feeding on the cambium layer just below the bark causes primary damage, according to Iowa State University.
This damage disrupts the flow of water and nutrients in the tree, resulting in progressive canopy thinning and branch death, usually from the outer or upper portions of the canopy downwards.
The decline usually lasts two to four years but can occur in as little as one year or as long as five years.
Epicormic shoots (suckers) form low on the trunk and main branches, and there is usually noticeable spotting of the bark caused by woodpeckers foraging for larvae.
Vertical cracks in the bark are occasionally observed, with galleries or tunnels visible beneath the split.
To manage trees infected or likely to be infected with EAB, there are two options.
You can either replace a failing/declining ash tree with another species or use preventative insecticide treatments to preserve and protect your ash tree.
Infected ash trees will die if preventive systemic insecticides are not applied. These preventive treatments are most effective on trees that do not show EAB damage and have a full crown.
To be eligible for treatment, trees must shed less than 50% of their canopy or die off less than 30% of their branches.
If the entire crown has visibly small leaves (thinning) and only large leaves are present in the center of the tree (on the stolons), the tree has already suffered too much damage for insecticides to “save” it.
Other causes of ash tree decline should be removed rather than treated, since preventing EAB damage will not reverse decline in trees affected by other diseases or insects.
Related article: Emerald Ash Borers strike again, Minnesota’s Hennepin County Ash Trees are hit
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