GRIFFIN, Ga.—Patti Bennett was looking out the window of her home office one morning two years ago when a swarm of green bugs flew out of the neighboring kudzu patch.

"I thought, 'What the hell is that headed at my house?' It was like a horror movie," says Ms. Bennett, a 53-year-old insurance underwriter who lives about an hour from Atlanta. She killed hundreds of bugs with spray, while thousands more released a musty, bittersweet odor in defense.

She scooped some bugs into a Tupperware container of alcohol and handed them to the local Home Depot specialist, an exterminator and a county agricultural agent.

Ms. Bennett was one of the first people in the South to report seeing Megacopta cribraria, an insect native to Asia that likely stowed away on a flight in 2009 and entered the U.S. through Atlanta's Hartsfield-Jackson International Airport, entomologists say.

Often a new bug brings nothing but bites and headaches for entomologists who race to limit the damage. But battle lines are being drawn over Megacopta cribraria.