SIOUX FALLS, S.D. (AP) — An insect that could threaten one of South Dakota's most populous tree species moved even closer to the state in the past year.

The emerald ash borer last year was found in Union County in southwestern Iowa. South Dakota State University forestry expert John Ball tells the Argus Leader newspaper that he thinks the Asian beetle will be found in South Dakota in five years.

The emerald ash borer was discovered in Michigan in 2002 and has since spread, killing tens of millions of trees in several states, including Minnesota. Beetle larvae tunnel under the bark of ash trees, destroying them.

Ball estimates that ash trees make up almost one-third of all the trees planted in South Dakota communities. They're also a common windbreak species in the state.

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