Bedbugs are back. They can infiltrate houses and apartments where unwitting humans and pets can carry them to their friends' and neighbors' homes. To combat them, there are bedbug-sniffing dogs and a variety of professional pest-control services as well as over-the-counter products.

A recently-published Ohio State University study put three commercially-available foggers to the test against bedbugs in the laboratory. Their conclusion: home bedbug foggers and bombs don't work. Use them and you'll waste your money, end up with a house full of insecticide and still have a bedbug problem.

Increased international travel and increased resistance of bedbugs to insecticides are two reasons often cited for the bedbugs' comeback.

The insecticides used in foggers (pyrethrins and/or pyrethroids) are of questionable effectiveness to begin with, are present at too low a concentration to kill the bugs, and simply do not penetrate into the cracks and crevices that bedbugs hide in. They typically killed fewer than 10% of the bedbugs in the laboratory.

Bedbugs nearly vanished from the developed world in the 1940s but have experienced a remarkable resurgence in the past 20 years. Increased international travel and increased resistance of bedbugs to insecticides are two reasons often cited for the bedbugs' comeback.

Adult bedbugs are flat, about the size of an apple seed and like to hide in cracks, crevices and fabric seams. Add in their increasing resistance to pesticides and you've got one extremely tough bug to kill.

The Ohio State researchers collected five strains of bedbug from Columbus, Ohio residences for their study. They also used the Harlan strain, a laboratory-maintained strain that is easily killed by pyrethroid insecticides and does not get the opportunity to become resistant, as their entire life is lived in the laboratory. An insecticide treatment that does not kill the Harlan strain is highly unlikely to be effective against real-world bedbugs.

Bedbugs were placed in Petri dishes or other plastic containers whose sides had been specially coated to prevent their escape. Half of the containers also contained small filter paper discs that the bedbugs could hide under, to simulate the cracks, crevices and folds that they normally hide in inside the home. Three foggers were tested: Hotshot, Spectracide and Eliminator. As specified on the fogger label, the treatment period was two hours, after which the room was opened and allowed to ventilate for 30 minutes. Bedbug mortality was then assessed immediately upon reentry, 24 hours later and 5-7 days afterward.

In addition, the researchers also tested one fogger (Hotshot) with the bedbug containers covered with thin cotton fabric, to better simulate the ability of bedbugs to hide in hard-to-reach places inside the home.

While effective against the Harlan bugs, the foggers otherwise proved largely ineffective, killing fewer than 10% of the bugs under most conditions tested. One exception was a bedbug strain called EPM, which showed about 60% mortality at 5-7 days when exposed to the Spectracide fogger in the open. This decreased to around 10% when filter paper discs were available for the bugs to hide under.

Even in the best case scenario, using the Spectracide fogger against unprotected EPM bedbugs, 40% of the bedbugs survived. And 40% of a bedbug problem is still quite a problem.

Perhaps most tellingly, even the specially bred Harlan bedbugs were largely unaffected when containers were covered with thin cotton fabric, with under 10% dead 24 hours later, compared to 97% when no covering was used. What chance would the foggers have against typical bedbugs hiding deep inside a mattress?

While a few professional pest control companies do use the insecticides that are in the home foggers, they use them in higher concentrations and generally as one part of a process that also includes steam treatment or freezing of bedbugs. And while there are certainly unscrupulous pest control companies, as with any type of company, the study strongly suggests that people relying on store-bought home foggers have no chance at all of winning the war on bedbugs.

People with a bedbug problem or those who simply like their bedtime tales on the gruesome side would do well to check out the University of Kentucky College of Agriculture's detailed fact sheet on bedbugs.

An article on the Ohio State study appears in the June 2012 issue of the Journal of Economic Entomology.