Cockroaches Are Crawling Closer To Invincibility From Pesticides

The common cockroach are developing powerful resistance to bug spray, making them alarmingly difficult to kill.

Some cockroaches are even becoming resistant to poisons they haven't even been exposed to yet.

The research from Purdue University has found that German cockroaches, found across the world, are developing cross-resistance to some of exterminators' most extreme insecticides.

The scientists studied three different sets of apartment buildings in Indiana and Illinois over the course of six months.

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The researchers caught German cockroaches and assessed which poisons they were most susceptible to -- they then used the insecticides that they believed would be most effective.

They had three different experiment conditions: in the first they used a rotation of three different classes of insecticide, in another they used a mixture of two and in the last they used only one insecticide that the cockroaches were particularly susceptible to.

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The experimenters had limited success in any of the conditions -- when they rotated three classes of insecticide, they were only able keep the cockroach population flat, but saw no reduction in numbers.

The mixture of two insecticides saw the cockroaches' number grow and the single-insecticide had mixed results, with one population all but eliminated and another where the population flourished.

The Purdue researchers found that certain cockroaches who had mutated to be resistant to particular classes of pesticides were quickly passing those traits on.

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Offspring of survivor cockroaches were gaining extensive resistance to the poisons, including new classes of insecticide that they hadn't even been exposed to yet.

Michael E. Scharf, one of the study's authors and an entomology researcher from Purdue, said this was occurring rapidly between generations.

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"We would see resistance increase four or six-fold in just one generation," he said.

Bryce Peters, an urban entomology expert from the University of Technology Sydney, told 10 daily that German cockroaches are particularly hardy because they breed incredibly quickly.

"German cockroaches have a really fast life cycle and someone has calculated that a single pair kept under the right conditions with unlimited food and water and breed conditions can produce abut 400,000 offspring per year," Peters said.

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This rapid life cycle means mutations which make them resistant to insecticides can be passed on rapidly to offspring.

Peters notes U.S. populations of German cockroaches appear to have different resistance to those in Australia and, for the moment at least, Australian cockroaches are still able to be killed by traditional insecticides.

However, he said this resistance is going to appear in Australia sooner or later, either by mutations occurring in German cockroaches on Australian soil or by being bred into the population from transient cockroaches arriving in shipping containers.

As for the cities most prone to German cockroach invasion, Peters notes these insects tend to thrive in sub-tropical regions and avoid the heat -- which is why Cairns may be relatively undisturbed by them but Sydneysiders may notice them quite frequently.