Scientists have suggested that cockroaches are quickly evolving to resist insecticides making them ‘almost impossible’ to kill.
Cockroaches are known for carrying diseases like salmonella and E. coli as well as just being genuinely terrifying.
To deal with them, pest controllers often mix different insecticides together in order to ensure that even if some roaches are immune to one they will be brought down by another.
Unfortunately, it seems like the creepy crawlies are catching up as their immune systems are strengthening to fight the poisons.
‘Cockroaches developing resistance to multiple classes of insecticides at once will make controlling these pests almost impossible with chemicals alone,’ explained Purdue University professor Michael Scharf, who led the study which has been published in the journal Scientific Reports.
‘This is a previously unrealized challenge in cockroaches.’
The research team examined the German cockroach (Blattella germanica) a ‘worldwide pest’ over the course of six months in some ‘housing facilities’ in Indiana and Illinois in the US.
It involved three different trials. In one treatment, three insecticides from different classes were rotated into use each month for three months and then repeated. In the second, they used a mixture of two insecticides from different classes for six months. In the third, they chose an insecticide to which cockroaches had a low-level starting resistance and used it the entire time.
‘If you have the ability to test the roaches first and pick an insecticide that has low resistance, that ups the odds,’ Prof Scharf said.
‘But even then, we had trouble controlling populations.’
The team found that by rotating three insecticides they were able to keep the population flat but not reduce it. When they were just using a mixture of two, the roach population skyrocketed.
In the experiment with the single-resistance group, researchers found there was little resistance to the chosen insecticide and they could almost completely eliminate the population.
But in another, about 10% had a starting resistance and the population grew from there.
That’s what gave them the idea that the roaches were evolving to deal with the insecticide.
‘We would see resistance increase four- or six-fold in just one generation,’ said Scharf.
‘We didn’t have a clue that something like that could happen this fast.’
The study points out that female cockroaches have a three-month reproductive cycle during which they can have up to 50 offspring.
‘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,’ the scientists say.
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