To the dismay of homeowners everywhere, cockroaches are famously tough. They can survive for over a week after their heads have been cut off, are resistant to radiation (though whether they can survive a nuclear bomb is still unproven), and are generally believed to be the inheritors of the planet once we’re all long gone.
So when these creatures would invade a home, an exterminator would turn to a powerful insecticide to do the trick. But now, researchers say that cockroaches can develop a resistance to pesticides at an astonishingly fast pace.
According to a study published in the journal Scientific Reports, some cockroaches can develop resistances to pesticides in a matter of months. Broad resistance to nearly all available insecticide classes was identified
Researchers from from Purdue University in Indiana looked into the German cockroach, a species found worldwide that only lives in human environments. They say the German cockroach can carry various antibiotic-resistant microbes — as well as E.coli — and produces allergens that can trigger or even help develop asthma.
The researchers started by testing insecticides on cockroach colonies in low-rise buildings in Indiana and Illinois over the course of six months — according to the study, low-income and inner-city communities are most susceptible to cockroach infestation. All the tested products were store-bought and applied with the help of professionals.
Even after attempting various combinations of the insecticides — including using just one, using a mix, or using all at the same time — the researchers found that over time, the cockroaches developed a resistance to whatever insecticide mix they were subjected to, and their survival rates went way up. Compared to a control group of cockroaches, that in some cases had a survival rate of near zero per cent, survivorship of the building cockroaches increased up to 80 per cent.
“Broad resistance to nearly all available insecticide classes was identified at both study sites,” the study said.
It also said the cockroach population increased in both buildings despite repeated use of the insecticide, and the mixture actually caused the cockroaches to begin dispersing and invading other previously-uninfested apartments.
The study said the resistance is most likely due to their fast reproduction cycle. A German cockroach matures at around 100 days old, at which point it’s ready to reproduce, potentially producing up to 50 eggs at a time. The cockroaches more inclined to survive an insecticide will pass on those traits to its offspring, who will do the same, and so on. After a few cycles, the small group of cockroaches become resistant to whichever insecticide it was subjected to.
“The unexpectedly poor performance of a majority of treatments in the field study suggested significant levels of starting resistance and/or selection for higher-level resistance in 4–6 months,” the study read.
A 2017 study out of Purdue University found that bed bugs were developing resistances to certain insecticides as well, and a 2018 study found that bugs were increasingly resistant to pesticides on farm crops, and the more pesticide was used, the more likely it would be for the insects to become resistant.
But not all hope is lost. The study did find that the most effective method of getting rid of cockroaches was to do a pre-treatment to determine which insecticide the colony would be least resistant to, and come back later to wallop them with the specific product.