Bed Bugs Resist Pesticides

A bed bug feeding on a human. CREDIT: Armed Forces Pest Management Board

Bed bugs are back, as many urbanites know. And while exterminators usually can eliminate bed bugs, a study shows that some of the pesky insects are developing resistance to pesticides.

Bed bugs feed on human blood.

There are several kinds, but the one best adapted to U.S. homes and hotels is Cimex lectularius. Bed bugs hide in bed frames and mattresses typically. They feed about once every five to 10 days, and not just at night. There are some reports that the bugs can harbor bacteria and diseases such as HIV and hepatitis B virus, but the insects have not been found to transmit disease.

The resistance study by toxicologist John Clark at the University of Massachusetts Amherst and his colleagues found that some bed bugs in New York City continued to thrive after being treated with pyrethroid insecticides, in particular deltamethrin, which attack their nervous systems.

A comparative sample of bed bugs from Florida showed no such resistance.

The New York bugs have acquired mutations in their nerve cells, which blunt the neurotoxic effect of the pyrethroid toxins used against them, according to Clark and his colleagues at Korea's Seoul National University.

The mutations affect sodium channels (resembling pores) in the neurons' outer membrane, where electrical nerve impulses are produced. In the past, these nervous system poisons could effectively paralyze and kill the bugs, but this is no longer always the case.

Using molecular techniques, the researchers sequenced genes related to the sodium ion channel's operation in both groups and identified two mutations found only in the resistant population. Similar mutations have been found in other pyrethroid-resistant insects and are likely the cause of the resistance in bed bugs, Clark and colleagues said.

The results are detailed in the November 2008 issue of the Journal of Medical Entomology.

264 times more resistant

Resistance means mutations are acquired over time by selection with pyrethroid, so the neuronal pores no longer respond to their toxic effects. Clark and colleagues found that these pores in New York City bed bugs are now as much as 264 times more resistant to deltamethrin.

This means that even if treated, New York City bed bugs can continue to feed on humans.

The researchers are not sure how widely this resistance has spread beyond New York.

"This type of pyrethroid resistance is common in many pest insects and the failure of the pyrethroids to control bed bug populations across the United States and elsewhere indicates that resistance is already widespread," Clark said.

The good news

Unless the researchers sampled every population of bed bugs in New York, it is unlikely that all NYC bed bugs are resistant to the insecticide, said Louis Sorkin, an entomologist at the American Museum of Natural History in New York.

Also, most pest control companies rely on more than one insecticide to combat bed bugs, he said. The ideal is to use a combination of chemicals that have different modes of action — perhaps one is good at killing the adults and nymphal stages immediately while another is better at lingering and killing bugs days later — and come from different chemical families, not just pyrethroids, Sorkin said.

Exterminators also have different ways to administer insecticides, which can make a difference — foams, powders, aerosols. However, over-the-counter aerosol bombs are not recommended. They just cause the bugs to scatter, Sorkin said, and fail to get inside cracks where bugs can hide.

"Some people don't like to say they have bed bugs. They try to take care of it themselves,” Sorkin said. But amateur attempts often just push the bugs away for a while and spread them into neighboring properties.

Many urban dwellers like to "trash pick," or go through the furniture and clothes that are left out on the curb before they are taken away by the garbage service. But nowadays, some of that furniture was put out as trash because it came from a home infected with bed bugs.

"People think, 'That's a nice piece of furniture,' and take it home. They get a bargain. The bed bugs are free, but controlling them is expensive," Sorkin said.

Integrated pest management

The state of the art in extermination is integrated pest management, Sorkin said, which means a multi-pronged attack that goes beyond spraying or misting insecticides.

Techniques include caulking, spackling and using other sealants to fill cracks and crevices, refinishing and sealing floors, injecting frozen carbon dioxide "snow" into electronics to freeze pests, re-painting walls and other surfaces, using low-moisture steam and clothes dryer heat to kill bugs, and injecting bug-killing dust into electrical outlets and switches. Sorkin and others recently collaborated with Jody Gangloff-Kaufmann and Cathy Pichler of the New York State IPM Program at Cornell University on an integrated pest management plan for homeless shelters in New York, which are susceptible to bed bugs.

"A lot of exterminations work because not all the populations here are resistant," Sorkin said. There are 400 products registered in New York for bed bug control, he said, although many of them are made of the same chemicals in different strengths, ratios and preparations.

There is even one company in Queens, New York, that works with moving companies for a total isolation approach for tough cases. Specially trained movers pack up your apartment and seal everything in plastic, Sorkin said, before taking everything to the company's fumigation center. Packages are opened and sealed up in an environment filled with toxic gas. Meanwhile, the empty apartment is also vacuumed and treated, and clothing is isolated and bagged.

"People have a lot of clutter in their apartments, but the more things are isolated, the better," Sorkin said.

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