Associated Press

State agricultural officials say an insect that has killed millions of ash trees has been found in five more Iowa counties, bringing the total to 50.

Officials said Thursday that the emerald ash borer has been confirmed in Benton, Buena Vista, Floyd, Howard and Warren counties.

Infected trees usually lose leaves at the top of the canopy and the die-off spreads downward. The trees usually die within four years.

The insects have killed tens of millions of ash trees and have been confirmed in 30 states. They are native to Asia and were first reported in the U.S. in Michigan in 2002. The insects were first detected in Iowa in 2010.

A federal quarantine restricts movement of hardwood firewood and ash articles out of Iowa into nonquarantined areas of other states.