A tiny iridescent-green bug is changing Iowa’s landscape by threatening one of the most commonly grown trees in cities, acreages and backyards.

The emerald ash borer (EAB), an invasive insect that’s native to China, has spread to 21 states, including Iowa, since it was first discovered in Michigan in 2002.

The insect feasts under the bark of ash trees, destroying the tree’s "plumbing" so the tree can’t take in water and nutrients, until the tree dies, explains Robin Pruisner, state entomologist with the Iowa Department of Agriculture and Land Stewardship (IDALS).

Once EAB is found in an area, it’s impossible to stop the spread, experts say. In...