The Invincible nature of cockroaches

                                                                    

As if cockroaches weren't already hard enough to get rid of, a new study from Purdue University suggests the German cockroach – the most common in the world – is quickly evolving to resist insecticides. 

The study, published in the journal Scientific Reports and led by Purdue professor Michael E. Scharf, was conducted over six months at two low-rise multi-housing units in Indiana and Illinois. In the study, Scharf and his fellow researchers tried three methods of controlling cockroach populations. 

Using the first method, they rotated three insecticides. In the second, they mixed two together. In the third, they pre-determined which insecticide a population wouldn’t have a resistance to, then used that particular insecticide over the course of six months. 

“We thought something was going to work,” Scharf told USA TODAY. “We tested ideas that had been out there for a long time, about either rotating or mixing or doing pre-monitoring to select products that have low resistance. So, we thought of those three different approaches, something would work.

Not only did two of the methods not work particularly well, but Scharf said he and his team could watch the roaches develop resistances “in real time.”

“It turns out, nothing worked really well, except one case where we could pre-monitor. The issue became – and this is where the whole headline comes from of roaches being invincible – we were surprised when we found they were cross-resistant to all these different insecticide classes. 

“We could determine that from our study, and we watched it happen in real time. We knew what they were being treated with, and we then watched them survive and the surviving populations become more resistant to all these different insecticides," he said.

Survivors passed on resistances to their offspring

German cockroaches are "known to spread at least 33 different types of bacteria, six kinds of parasitic worms and at least seven other human pathogens," according to the National Pest Management Association. 

Also, "the saliva, droppings and decomposing bodies of cockroaches contain proteins that trigger allergies and increase asthma symptoms, especially in children," according to the organization. 

German cockroaches can breed at a rate of up to six generations per year, according to the NPMA. 

How quickly the roaches developed resistances shocked Scharf.

“We’re finding that they can adapt so quickly,” he said. “Pest managers have to be thinking about how to stay ahead of them. So, they’re constantly going to be evolving every time you treat them with insecticides. You’re left with survivors, no matter what.” 

To make matters worse, he said:  “They develop these specific physiological mechanisms to one type of insecticide and those same mechanisms will give them resistance to other things they haven’t been exposed to yet, because of the similarities in the insecticides."

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So, what’s the solution if roaches can adapt to insecticides? Scharf recommends a non-chemical approach, such as glue traps, pest-control vacuums and “sanitation and exclusion.”

“We recommend, for residents, they can be taking out their trash on a daily basis," Scharf said. "In low-income scenarios, people have bigger problems than cockroaches or taking out their trash each day, typically. But we’re recommending that people practice good sanitation. 

“Then, just keeping roaches from moving between apartments is a big one, too. Putting exclusion devices under doors and making sure the plumbing doesn’t offer a highway between apartments for cockroaches to move through, that kind of thing.” 

How you take care of your pets can play a role, too. 

“We recommend that people just feed their pets once per day and be sure that their pet eats all the food and the roaches don’t," he said.