Nature

Cockroaches are so tough they Develop Resistance to Pesticides They Haven’t Even met

You’ve got to hand it to the cockroach. Human progress might be an apocalypse for other animal species, but not these guys. And now it’s clear they’re having a jolly good laugh at our puny attempts to control them with pesticides.

A study on how quickly populations of German cockroach (Blattella germanica) bounce back after being doused with several classes of insect killer has revealed they can evolve a general resistance to pesticides they’ve never even encountered.

Researchers from Purdue University set up an experiment to evaluate how roaches evolve pesticide resistance over successive generations, hoping to determine which methods for eradication might be optimal.

The take-home advice for those keen to spray is that the single best method for keeping on top of your pest problem is… building a biology lab in the basement and routinely running tests on your infestation.

“If you have the ability to test the roaches first and pick an insecticide that has low resistance, that ups the odds,” says entomologist Michael Scharf.

“But even then, we had trouble controlling populations.”

Got that? You can already hear the germ-shedding freeloaders tittering from the shadows.

Of course, most of us aren’t entomologists with experience in determining insecticide susceptibility. So, just how screwed are we?

Scharf and his team visited low-rise apartments in Danville, Illinois, and Indianapolis, Indiana to trap some specimens. They used baby-food jars baited with bread and beer and came away with a variety of B. germanica strains. These were kept safe in the lab in two separate populations and studied for resistance.

Back out the field, the apartments were given one of three treatment methods once per month over a six month period.

The first method involved individually applying one of three different classes of insecticide on a monthly rotation. For the second, a mixture of two of the pesticide classes was applied for the entire period. And for the third, the team chose an insecticide that matched the lowest resistance identified in the populations back in the lab.

It turns out sticking to a random mix of a couple of pesticides is a pretty bad idea. Method two simply didn’t work, with cockroach populations continuing to thrive over the course of the treatment.

Meanwhile, rotating insecticides didn’t cure the apartments of infestations, but it did keep them relatively quiet, at least while routine spraying took place.

If you can find out what your cockroach’s kryptonite is, you just might have a fighting chance. In the Indianapolis apartments, the team very nearly won the battle using a pesticide called abamectin.

Danville wasn’t so lucky. Scharf’s team calculated their target roach population there had a 16 percent resistance level to the poison, so the single-chemical treatment failed to deliver a blow.

Back in the lab, their two caged populations helped the researchers pull apart what they saw in the field. By testing pesticides in the lab, they could work out how long it took for generations to breed back into previous numbers.

Answer: not long enough.

If even a handful of resistant cockroaches survive that first treatment of one or even multiple pesticides, their offspring will reclaim the land for super-fun-happy times and a carefree existence dancing joyfully in their poisonous paradise.

Rotating pesticides will dampen those spirits a touch, but resistance will always win the day.

Most shocking of all, it turned out that by developing a resistance to one class of pesticide, the cockroaches had a better chance at surviving another one altogether. Field-collected insects that had been hit monthly with just abamectin were also now more resistant to the other two pesticides used in the study.

“We would see resistance increase four- or six-fold in just one generation,” Scharf said.

“We didn’t have a clue that something like that could happen this fast.”

Exactly how they do this is a mystery. Unlike superbugs, the biochemical mechanisms of cockroach resistance haven’t been a high priority, and have never been heavily researched.

The lesson here is to not get lazy when it comes to pest control, and think strategically about cockroach eradication. We could find new pesticides, perhaps, and hope that evolution cuts us some slack.

Or maybe it’s time we made peace. When all other food sources collapse, you might be grateful you did.

This research was published in Scientific Reports.

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