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Not Even Chemicals Can Stop the Indomitable Cockroach

A new study suggests it will soon be “almost impossible” to control the insects with chemicals alone

I, for one, welcome our new insect overlords. (John Obermeyer/Purdue Entomology)
smithsonian.com

Cockroaches are notoriously resilient creatures. Capable of living headless for weeks on end, holding their breath for around five to seven minutes and even surviving nuclear radiation, the insects serve as formidable foes for humans hoping to rid their homes of pesky roach infestations. But these tenacious qualities aren’t the only signs of the animal’s seeming invincibility: A new study published in the journal Scientific Reports suggests cockroaches are becoming increasingly resistant to pesticides, paving the way for a near-future in which it will be “almost impossible” to control the pests with chemicals alone.

The research, conducted by a team of Purdue University entomologists, centers on a specific species dubbed the German cockroach. (Per the University of Florida’s “Featured Creatures” portal, the animal, a ubiquitous pest that lives exclusively in human environments, is “the cockroach of concern, the species that gives all other cockroaches a bad name.”)

As Brian Resnick explains for Vox, the researchers found that cockroaches, much like bacteria developing resistance to antibiotics, can evolve resistance to insecticides. And that’s not all: Once the roaches survive one strain of insecticide, they also become better equipped to resist multiple classes, or varieties distinguished by factors including toxicity and chemical composition, to which they have not been previously exposed.

“We would see resistance increase four- or six-fold in just one generation,” lead author Michael Scharf says in a statement. “We didn’t have a clue that something like that could happen this fast.”

To gauge the extent of the insects’ indestructibility, Scharf and his colleagues experimented with different extermination strategies at roach-infested apartment complexes in Illinois and Indiana. According to Gizmodo’s Ed Cara, the team sprayed one building with a rotating group of three insecticides, switching strains once a month for six months, and another with two insecticides at the same time monthly. At the final site, the researchers laid out abamectin gel baits—a class the cockroaches had previously shown low resistance to—once a month.

The first rotating insecticide test failed to reduce the apartment building’s roach population but kept it at a flat rate. The second, meanwhile, failed completely, leaving the cockroaches free to flourish, as Jason Murdock writes for Newsweek. The final strategy yielded mixed results. Although the scientists managed to all but eliminate the population with a low starting resistance, a separate group in which 10 percent of the population demonstrated starting resistance to the gel bait actually grew in size.

“If you have the ability to test the roaches first and pick an insecticide that has low resistance, that ups the odds,” Scharf says in the statement. “But even then, we had trouble controlling populations.”

Adding to the problem, U.S. News & World Reports Cecelia Smith-Schoenwalder notes, is the fact that pesticide-resistant cockroaches pass down this immunity to offspring. According to the Purdue press release, female cockroaches have a three-month reproductive cycle and can produce up to 50 offspring at a time; the statement continues, “If even a small percentage of cockroaches is resistant to an insecticide, and those cockroaches gain cross-resistance, a population knocked down by a single treatment could explode again within months.” Vox’s Resnick explains that cockroaches can evolve behavioral resistance, learning to avoid pesticides and passing down this cautionary gene to future generations.

Cockroaches are more than just household nuisances. As Resnick reports, the insects shed “roach dust” capable of triggering or worsening asthma symptoms and carry pathogens such as salmonella and E. coli.

To best manage roach infestations, Scharf suggests physically removing the insects with the help of special vacuums and sticky traps. Although these methods are more expensive than chemical options, they are more likely to offer long-term benefits, including lessening cockroaches’ exposure to pesticides and paving the way for these extermination measures to regain effectiveness.

Scharf concludes, “Some of these methods are more expensive than using only insecticides, but if those insecticides aren't going to control or eliminate a population, you're just throwing money away.”

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