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Cockroaches evolving against chemicals

Chase Winter
July 2, 2019

Researchers say the findings mean it will become impossible to exterminate the common cockroach with chemicals alone. Female cockroaches have dozens of offspring in a three-month reproductive cycle.

Blattella germanica
Image: Picture-Alliance/Photoshot

The German cockroach is rapidly developing resistance to an array of powerful insecticides used for extermination, making it nearly impossible to control the nasty pests with chemicals alone, a new study has shown.

Blattella germanica L., a cockroach carrying dozens of infectious bacteria and whose infestation of homes can trigger allergies and asthma, is a global pest living in human environments.

Read more: WWF highlights drastic drop in German insect population

Each class of insecticide works in a different way to kill cockroaches. Exterminators will often use insecticides that are a mixture of multiple classes or change classes from treatment to treatment. The hope is that even if a small percentage of cockroaches is resistant to one class, insecticides from other classes will eliminate them.

However, a study published in the journal Scientific Reports found that the German cockroach is developing cross-resistance to multiple chemicals, meaning that offspring are gaining resistance to insecticides even if they had not been exposed to them and not had prior resistance.

Read more: How to stop an insect apocalypse

"We would see resistance increase four- or six-fold in just one generation," said Michael Scharf, the lead of the study conducted through Purdue University. "We didn't have a clue that something like that could happen this fast."

"This is a previously unrealized challenge in cockroaches," said Scharf, who conducted the research at apartment buildings in the United States. "Cockroaches developing resistance to multiple classes of insecticides at once will make controlling these pests almost impossible with chemicals alone."

Female cockroaches have dozens of offspring in a three-month reproductive cycle. Even if a fraction of cockroaches are resistant to an insecticide, and they or their offspring acquire cross-resistance, then even when a population is reduced, it can quickly explode again within months.

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