Friday 6 December, 2019

Cockroaches becoming impossible to kill using insecticides - study

Stock photo of cockroaches.

Stock photo of cockroaches.

Hate cockroaches? If so, we have some bad news. Scientists are warning that the house-infesting pests are getting harder to kill and may soon become impossible to get rid of using insecticides alone.

Researchers from Purdue University in the United States found that German cockroaches - one of the most common species of household cockroaches - are quickly becoming resistant to pesticides.

The study saw the Professor Michael Scharf-led research team using three different methods of controlling cockroach populations at multi-unit buildings in Indiana and Illinois over six months, according to a press release on the university's website.

According to the researchers, different classes of insecticides work in different ways to kill cockroaches. They noted that exterminators often use pesticides that are a mixture of multiple classes or change classes from treatment to treatment, with the hope that even if a small percentage of a cockroach population is resistant to one class, insecticides from other classes will eliminate them.

In the study, one treatment involved the rotation of three insecticides from different classes into use each month for three months and then repeated. In the second treatment, researches used a mixture of two insecticides from different classes for six months. And, in the third, they used a single pesticide to which cockroaches had low-level starting resistance and used it the entire time.

Of the three treatments, only the third managed to reduce the cockroach population, according to the press release.

Rotating three insecticides, the researchers were able to keep cockroach populations flat over the six-month period, but they could not reduce them. The two-insecticide mixture did not work, and cockroach populations flourished, the release said.

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

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

The release noted that in one of the single-insecticide experiments, Scharf and his colleagues found that there was little starting resistance to the chosen insecticide, and they were able to all but eliminate the cockroach population. In the other, there was about 10 per cent starting resistance but, in that experiment, populations grew.

According to the researchers, the surviving cockroaches pass on resistances to their offspring.



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