Inbreeding To Blame For Bedbug Renaissance

Presenting at a meeting of the American Society of Tropical Medicine and Hygiene, researchers said bedbugs can survive many generations of inbreeding, allowing one pregnant female to cause a building-wide infestation. Biologist Rajeev Vaidyanathan discusses that study, and another on pesticide resistance.

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JOE PALCA, HOST:

Next up on this program, bedbugs, as you may have heard, are having a renaissance in cities all over the United States, in bedrooms, of course, but also in department stores, office buildings, movie theaters, and they're not cheap to get rid of. My next guest estimates New York City alone spends anywhere from 10 to $40 million a year to control them. What's behind their wild success? One reason, which you hopefully haven't experienced firsthand, is their ability to withstand our most common chemical weapons.

Another has to do with their remarkably strange sex lives. Two topics covered at this week's meeting of the American Society of Tropical Medicine and Hygiene in Philadelphia. My next guest is here to report about the bedbug symposium he organized, Rajeev - I'm sorry - Rajeev Vaidyanathan is an associate director of the Vector Biology at SRI International in Harrisonburg, Virginia. He's here in our New York studios. Welcome to the program, SCIENCE FRIDAY, Dr. Vaidyanathan.

DR. RAJEEV VAIDYANATHAN: Thank you.

PALCA: So I guess we have to start, you know, we can't leave anybody hanging with this sex business, so tell us, what is it that's interesting about the sex life of bedbugs?

VAIDYANATHAN: There's a lot that's interesting about the sex lives of bedbugs. First of all, bedbugs themselves, in the dark, I guess, everything looks like a female bedbug. And so male bedbugs don't really discriminate, and they will attempt to mount and copulate with blood-fed immatures, blood-fed males and blood-fed females. That's just the beginning of it. On top of that, the male bedbugs themselves will penetrate the female's body cavity and will actually try to fertilize from the inside rather than going through an outside.

PALCA: Ouch.

VAIDYANATHAN: The term for sex among bedbugs is known as traumatic insemination.

PALCA: Yikes. But apart from their proclivities, is there something about their mate selection that's making this problem worse?

VAIDYANATHAN: True. Work done by Coby Schal and Ed Vargo at North Carolina State University tested three different hypotheses, basically where are bedbugs coming from and why are there so many of them in the U.S. now. The question was did bedbugs originate from a U.S. population and radiate outward or was there an individual introduction into the U.S. from outside and did that radiate or have there been multiple introductions from multiple sites over time. What Coby and Ed found was that multiple introductions over time account for the diversity in bedbug populations in North America. That's part of it.

When you look across populations, you'll find a lot of genetic diversity. However, if you look at one population of bedbugs, say, it's one infestation in one apartment, in one building, there's pretty much one grandmother, one Eve that determined that entire infestation. Her sons and daughters mate with one another so there's extreme inbreeding. When they have progeny, those brothers and sisters will mate with one another. And so the degree of genetic diversity within any one bedbug population is very, very low.

What Coby and his colleagues at North Carolina and collaborators at Rutgers found is that even within an apartment building if you have two populations of bugs, they don't even mate with one another. So you could have line from one grandmother that occupies several apartments. You might have a line from a different grandmother that occupies a separate set. But the two of them don't actually mate with each other. So the degree of genetic diversity - or rather the degree of mating between those two populations is about as much as you'd get between one population in New York and another in Vancouver.

PALCA: So what are the implications of this for control strategies?

VAIDYANATHAN: Absolutely. I think two points that came out at the American Society of Trop Med Hygiene meeting were, one, the degree of inbreeding and, two, the degree of insecticide resistance. Consider that work done by Ken Haynes and colleagues at the University of Kentucky has found that basically every bedbug population that they've looked at - or I should say almost every one they've looked at is highly resistant to the most common class of insecticides that are use for bedbug control.

Now, if populations that are resistant are only mating with themselves, their progeny only mate with themselves and so on, then there's an extremely conservative selection for those genes which are resistant to insecticides. So these two stories go hand in hand.

PALCA: I see. We're talking bedbugs. And if you have a question of if you're itching yourself, give us a call. 800-989-8255, 1-800-989-TALK. What about this idea of inbreeding? Most people think or were taught that inbreeding decreases the vitality of the species. And this doesn't seemed to be the case with bedbugs.

VAIDYANATHAN: It doesn't. Frankly, the mechanism is not known. Part of that may well be that inbreeding in this case has a selective advantage in that it's actually choosing for genes, say, for pesticide resistance. But beyond that, frankly, we're not sure.

PALCA: Hmm. What about your own research? You're doing some interesting work trying to figure out where infestations are occurring.

VAIDYANATHAN: That's correct. In a recent symposium, the two major deficits in bedbug research were identified as quick and efficient detection, and effective control mechanisms. So our work at SRI International is focusing on identifying the volatile compounds that are present in bedbug samples that, basically, give you a signature perfume. And if we can identify what the constituents of that signature perfume are, we can use that to enhance our detection of bedbugs. And two, we can also use that to saturate traps and enhance collection and control.

PALCA: And I think we have time for one quick question from one of our listeners. Let's go to Eric(ph) in Kansas City. Eric, welcome to SCIENCE FRIDAY.

ERIC: Yeah. Howdy. I'm going to Europe here in a few months, and I was wondering if there was anything I can take, I guess, for preventive maintenance for hotels.

(SOUNDBITE OF LAUGHTER)

PALCA: Preventive maintenance, a good way to put it. Dr. Vaidyanathan?

VAIDYANATHAN: You know, over 40 percent of Americans have changed their behaviors in hotels because of bedbugs. There is no one thing in terms of preventive maintenance. The best thing that - the two best things you can do, really, are: one, kind of check ahead of time on bedbug registry.com. And if you're there, check under the beds for the telltale fecal spots. What I always do - and number two - and when I actually go, I keep my luggage in the bathroom.

(SOUNDBITE OF LAUGHTER)

PALCA: Why?

VAIDYANATHAN: Because there's a less chance of having bedbugs in the bathroom than actually in the bedroom itself.

PALCA: Huh. And is there...

(SOUNDBITE OF LAUGHTER)

PALCA: ...is that a concern that people should have? I mean, as in traveling or just in places where there are infestations?

VAIDYANATHAN: In the last 10 years - and this is a very important point you bring up. In the last 10 years, 25 percent of hotels in the United States have had bedbugs - have sprayed for bedbugs. However, that is a very misleading number. Less than 1 percent, in fact, 0.6 percent of all the rooms have had bedbugs in them. That really points to the importance of precise detection.

If you detect bedbugs in a hotel, and you give off an insecticidal bomb in the lobby, or you indiscriminately spray in every room, it's a waste of money. It's ineffective. And it's really a disastrous PR. It's very important to determine exactly where they are and to target that area.

PALCA: OK. Let's take another call now and go to Maya in Acton, Massachusetts. Welcome to SCIENCE FRIDAY. You're on the air.

MAYA: Hi. I'm calling to inquire whether I should be concerned when my sister comes to visit from Brooklyn, where her building occasionally has bedbugs.

PALCA: Huh. OK. What about?

VAIDYANATHAN: I think you should be concern that your sister lives in Brooklyn.

(SOUNDBITE OF LAUGHTER)

MAYA: That is a problem.

PALCA: Now, wait a minute. Wait a minute. Wait a minute. We're in New York, pal. You're going to walk out of here. You're going to get in trouble.

(SOUNDBITE OF LAUGHTER)

PALCA: No, seriously. Is there any concern - is there anything - well, is there any concern?

VAIDYANATHAN: Bedbugs don't travel on an individual. Bedbugs are wingless, and so they're entirely dependent on being carried either on upholstery, on a bed. And occasionally, they do migrate into luggage. It's important to distinguish between detection and infestation. And if there's one bedbug, it's not a big deal. And unfortunately, people do tend to overreact to a single bedbug. However, it's the infestations that can actually lead to bites, to redness and to actually psychological distress. If your sister is coming from Brooklyn, what you might want to try is to take a travel lint roller and go around the outside of the luggage. Anything that's on it you might be able to pick up.

PALCA: Wow.

MAYA: Is her laundry OK? Should I be concerned with her clothing?

VAIDYANATHAN: If - you know what?

PALCA: Aesthetically or bedbugs?

VAIDYANATHAN: That's right.

MAYA: She does laundry at my house, mind you.

VAIDYANATHAN: And you know what? That's very good because the two best things to do for actually controlling and reducing bedbug populations in the house are, number one, getting rid of clutter and vacuuming. And number two, drying the clothes on the hottest setting in the dryer. It's not the hot water of the wash, but it's really keeping them in the dryer.

MAYA: Dryer.

PALCA: OK. Maya, thanks for that call. What about the, you know, the decision to stop using DDT? Has that taken a weapon away from what might be an effective control strategy?

VAIDYANATHAN: I think Ken Haynes from the University of Kentucky made a very good point, that by the time DDT was commonly use for bedbug control, bedbugs were already resistant to it.

PALCA: So...

VAIDYANATHAN: The first instances were in 1947, 1948. And today, bedbug resistance to insecticides and to DDT in particular has been documented in over 18 countries.

PALCA: OK. I think we have time for one more quick call and go to George in Cincinnati. Welcome to SCIENCE FRIDAY. You're on the air.

GEORGE: Yeah. Hi. A great show. I enjoy it very much, especially this particular topic. I'm an airline pilot and I'm on the road all the time. And it's a real concern for me with bedbugs. But I wanted to ask, really, two questions. One, can animals, can dogs really detect bedbugs within a residence? And two, if, for instance, you're traveling and you wake up, and you find that you've been beaten and there are bedbugs in the room, what should you do? Should you just destroy everything you have and come home with a clean set of clothes? And I'll take your answer off the air. Thank you.

PALCA: OK. Thanks very much.

VAIDYANATHAN: Great. So for question number one, yes, there - canines are used to detect bedbugs. Just as dogs have been trained to find bombs or drugs, they can also sniff out bedbugs. The problem with that is that there are a high level of false positives. Sometimes they - you think they detect it when they don't. And it can get really expensive. So although they can be useful, it's not a sustainable long-term solution.

About your second question. If you do find that you've been beaten, as I mentioned to the previous caller, probably the best thing you can do is, when you get home, wash everything on a hot cycle, and then put it at the hottest setting of your dryer for the longest time, and be careful of the seams of your luggage, which is where the bedbugs will hide.

PALCA: All right. Well, I'm afraid we have to leave our bedbug primer there. Rajeev - I'm sorry - Vaidyanathan, is the associate director of vector biology at SRI International in Harrisonburg, Virginia. Thanks very much for joining us.

VAIDYANATHAN: It's been my pleasure.

PALCA: I'm Joe Palca, and this is SCIENCE FRIDAY from NPR.

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