CHAPEL HILL, N.C. — Don't let them bite, the old rhyme says.

But growing numbers of North Carolinians may not have a choice when it comes to bedbugs. Once largely eradicated in the United States, the tiny insects are making an itchy, bloodsucking comeback.

Scientists and pest control companies say it may be linked to increased international travel, the ban on DDT and changed pesticide practices.

"We just don't really have anything in our arsenal that's effective against bedbugs anymore," said Donnie Shelton, owner of Triangle Pest Control.

Since Shelton started his business 18 months ago, calls for bedbug treatment have risen from one a month to as many as five a week, he said.

And old social stigmas about the bloodsucking pests linger, experts say.

"There's a lot of folks who don't bother to call us. They're embarrassed. The social connotation goes back to the early 1900s; they were associated with slummy places. And that's not the case now," said Michael Waldvogel, an entomologist with the N.C. Cooperative Extension. The bugs are a problem all over the country, experts say.<

Waldvogel says he has gotten reports of bedbugs from across the state — some tied to vacationers bringing them home from beach houses or hotels.

Bedbugs are tiny and persistent and don't just live in beds, Waldvogel said. They can hide behind headboards, in carpeting and tiny crevices in furniture. They've even been found under clock radios and lamps, he said. "One guy found them, I think, in a microwave oven in a kitchen."

And getting rid of them isn't simple.

Waldvogel advises hiring a skilled professional, in part because it's important to consider carefully what chemicals to spray in living areas such as bedrooms.

"The person who treats your home should spend more time with a flashlight than a sprayer," he said.

At Bayer Environmental Science in Research Triangle Park, entomologists are working to develop new techniques and make existing products more effective against bedbugs. Training is a big component of Bayer's work, said Byron Reid, product development manager.

"There are thousands of pest control professionals out there who have never had to do the bedbug job," he said. Bayer runs a training facility for pest control operators in Clayton, N.C., where it can recreate bedrooms and apartments to train in proper techniques.

But getting rid of the pests isn't easy, and vigilance is key to avoiding them.

Travelers can reduce the chances of a bedbug infestation by checking for the bugs and their droppings in hotel rooms. Keeping luggage and clothing off the floor can help, too.

If a home does become infested, Shelton said, it's a long, expensive process to get rid of the bugs.

The first step, he said, is a good mattress cover. A cheap one won't cut it because the bugs can bite through them. Then Shelton's crews treat with pesticides.

"We can only treat so much with chemicals," he said, because of the bugs' ability to hide. "We kind of kill them by starving, really." And bedbugs can theoretically lie dormant for more than a year without food.

The final step is bagging all laundry and linens and drying them on high heat to kill the pests, Shelton said.

"Depending on how bad it is, you can expect to spend anywhere from $700 to $1,500," he said.

Virginia Tech entomologist Dini Miller says modern bedbugs are resistant to insecticides and ignore substances that repel pests such as roaches. "We kind of have these superbedbugs now that are being spread," she said. Miller said bedbugs can carry pathogens but don't transmit them to humans.

Scientists and exterminators say the bedbug resurgence is probably because of a combination of factors, including the ban on DDT insecticide in the early 1970s.

Low-cost international travel also could be a factor.

But scientists aren't sure why bedbugs are making a comeback, and the true scale of the bedbug problem isn't clear.

Warren Booth, a post-doctoral researcher at N.C. State University, said people need to be aware of the potential. "Anywhere humans are, theoretically bedbugs can follow," he said. He's had reports of the insects being found even in airport lounges. And there's an economic side too.

"If the general public were aware of how many hotels have had bedbugs reported in them, it would really affect business for a lot of these companies," he said.