Science

The new "superbugs": Cockroaches evolve resistance to pesticides they haven't even encountered

The new "superbugs": Cockroach...
A cockroach feeds on an insecticide in the lab portion of new experiments at Purdue University
A cockroach feeds on an insecticide in the lab portion of new experiments at Purdue University
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A cockroach feeds on an insecticide in the lab portion of new experiments at Purdue University
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A cockroach feeds on an insecticide in the lab portion of new experiments at Purdue University

It's bad enough that bacteria are quickly developing resistance to our best antibiotics – now it looks like another kind of bug will soon earn the "super" moniker. Cockroaches have been known to develop resistances to individual insecticides for decades, but new research has shown that they're also able to rapidly develop cross-resistance, even to chemicals that they've never been directly exposed to.

Unfortunately, there's no one insecticide that's able to wipe out all cockroaches. Some of the bugs have natural immunities to certain chemicals, letting them survive the exterminator's wrath that may take out the rest of a colony. And as the principal of natural selection goes, those survivors go on to be the only ones to breed, passing those genes on and ultimately immunizing the whole population against that poison. It's the same thing that's happening with bacteria and antibiotics.

To get around that, exterminators have traditionally used a mix of different classes of insecticides. That way, even if some roaches are immune to one of the chemicals, the other poisons should wipe them out. At least, that's the idea behind how it should work.

For the new study, researchers from Purdue University tested what was the most effective method. Over six months, they subjected cockroach populations in several buildings to three different insecticide treatments, and compared the results. Before the study, roaches were caught from each location and studied to determine which classes they were resistant to, informing the scientists' choices.

One treatment cycled through three different classes of insecticides, alternating each month in an ABCABC pattern. In the second treatment plan, the team mixed insecticides from two different classes, and used that mix for the entire six month period. And in the third, the team chose one insecticide which the local roaches had the least resistance to and used that the whole time.

The results were mixed, but fascinating. The rotating insecticide treatment was found to keep roach numbers flat, but wasn't able to reduce them. The two-insecticide mix wasn't effective at all, with populations flourishing in spite of the treatment.

Experiments with the single, targeted insecticide were varied. In one, the bugs were basically wiped out, but in another test populations actually grew.

At the end of the experiment period, the researchers caught some of the remaining cockroaches and studied them in the lab. As expected, they found that many had resistance to the insecticides used. Worryingly though, they also seemed to have gained resistances to other classes of the poisons, even if they hadn't been used. This kind of cross-resistance could make cockroaches even harder to kill in future.

"This is a previously unrealized challenge in cockroaches," says Michael Scharf, lead author of the study. "We would see resistance increase four- or six-fold in just one generation. We didn't have a clue that something like that could happen this fast. Cockroaches developing resistance to multiple classes of insecticides at once will make controlling these pests almost impossible with chemicals alone."

The team says that the most effective method of would be to combine these insecticides with other forms of pest control, such as bait traps and good old-fashioned cleaning up after yourself.

The research was published in the journal Scientific Reports.

Source: Purdue University

4 comments
Douglas E Knapp
I have battled this thing and the winning treatment is to get rid of all water sources in the house. This mean water condensing on pipes, tollets, water catcher under fridges etc. Never let them get water and when they do make sure it is salty and also give them stuff to make them thirsty. Next find all the hiding spots and shut them down. You have no look very carefully because they can find all sorts of cracks. Once you have all the cracks shut, come down at night and quickly turn on the lights and watch were they run too. Shut these places down also. After a few weeks of this, you will have no more roches save what you bring home with you.
Expanded Viewpoint
Doug, That sounds like a good strategy, but exactly how did you implement it? How do you keep the roaches from getting to water condensing on something, especially under a freezer or refrigerator? Knowing how to block them off from getting to condensate on a cold porcelain sink or toilet would also be very good to know. As for myself, I mixed up a batch of white flour, brown sugar and baking soda in equal portions, then wet it to a paste and put it into an empty cat food can and let it dry out. Then, I placed the can on edge so it would be easy for the bugs to get into it and feed. The baking soda when it hits their stomach acid turns into Carbon Dioxide gas and since they seem to have an inability to belch, it ruptures their stomach. Our roach problem has gone way down since doing this. The roaches around our garbage cans are virtually nonexistent now. Mixing in some maple syrup instead of the brown sugar might make the mix more attractive to them. I will try that on the next batch of roach baits I make up. Using this type of chemical approach is far better than direct poisons which harm the environment. Randy
Statutes of Liberty
Really sick of 'people' claiming they have found something amazingly 'evolutionary' about what cockroaches can do !! There is absolutely nothing evolutionary about a cockroach that eats just about any decaying organic matter and has always been naturally resistant to a whole range of toxins contained in the decaying matter it consumes. Ever since I can remember experimenting with different ways of killing roaches there's only ever been 2 ways of finding an effective terminator Either a poison that paralyses its body parts or a poison that shuts down either its '13 chambered' heart or a vital organ or a combination of the above. Cockroaches are 'genetically designed' to resist a range of toxins so scientists tried adding a paralysis to the mix to stop it from moving It is a well known fact that if a cockroach can continue to move its legs and body parts it can eventually release the poison out its ring of tubules called the gastric caecae, which secrete digestive juice or release the toxin out its anus which does with toxins in the food it digests Try a little more research 'people' there is no scientific evidence of it having evolved at all !!
Expanded Viewpoint
Well I've never dissected any bugs, and have never seen any "Gray's Anatomy" type of illustrations of cockroaches, so I can't say if the gut bomb approach is a viable one or not. But, after deploying the baking soda mix, there are very few, if any, roaches under our trash cans. How do you explain that? What about using an acid and resin mix that eats though their out skeleton, causing them to bleed out? Doesn't that work also without putting neurotoxins into our environment? Randy