Cockroaches Are Evolving To A Point Where They’ll Be Nearly Impossible To Kill

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A new study has found that German cockroaches are developing cross-resistance to numerous insecticides.

Researchers are unable to reduce cockroach numbers during a six-month study period. They found the insects’ resistance increased up to six-fold within one generation.

Lead author Michael Scharf, of the Department of Entomology at Purdue University, said in a statement.

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


The researchers tested out different treatments of three insecticides – abamectin, boric acid, and thiamethoxam – in numerous cockroach-infested apartments across Indiana and Illinois over six months. In one treatment, three different insecticides were rotated each month for three months and then repeated. In a second, they used two insecticides from different classes for six months. In the third, they chose one insecticide to which cockroaches had low-level starting resistance.

Regardless of the different chemical combinations, the researchers were unable to reduce the size of their population. In the single insecticide treatment, populations grew with around 10% as individuals starting to evolve resistance. With the two insecticide treatments, the cockroach populations skyrocketed. The three-pronged attack managed to maintain the number of cockroaches but it was unable to reduce it.

Lab tests showed that a considerable share of the cockroaches and their offspring had become “essentially immune” to pesticide.

Cockroaches can pump out up to 50 offspring during their three-month reproductive cycle, so only a small portion of their offspring need to develop cross-resistance, survive, and reproduce for a population to bounce back and boom within a couple of months.

The researchers say their findings highlight the need for combining chemical treatments with traps, improved sanitation, and vacuums to control cockroaches, rather than just relying on insecticides.