YANKTON, S.D. (AP) — South Dakota's Game, Fish and Parks Department is reminding campers to follow quarantine restrictions on firewood to stem the spread of an invasive insect.

Emerald ash borers were confirmed for the first time in South Dakota in Sioux Falls last May, the Yankton Daily Press & Dakotan reported. The destructive insect has killed millions of ash trees in more than 30 states, the department said.

South Dakota has banned wood from outside the state. Officials have instructed that wood products from Minnehaha County and parts of Lincoln and Turner counties be kept in those areas, unless they've been deemed safe to move.

The state has also banned outside wood from entering the quarantine area.

"When the restriction went into effect earlier this summer, we did see quite a few people still bringing in out-of-state firewood and people bringing in firewood from the quarantine area," said Jake Manning, park director for the Lewis and Clark Recreation Area near Yankton. "As soon as we started enforcing the restriction — taking a closer look at it, talking to people, getting them educated — it dropped off."

Manning said they've yet to find anything with signs of the ash borer.

The restrictions will remain in place year round since the insects can survive the winter.

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Information from: Yankton Press and Dakotan, http://www.yankton.net/