Cockroaches are stepping up their defenses againstthe poisons designed to kill them.
A new study has found that German cockroaches, themost common species of the insect in the world, aredeveloping cross-resistance to numerousinsecticides.
Not only were researchers in some cases unable toreduce cockroach numbers during a six-month studyperiod, even when combining different insecticides, but they found the insects' resistanceincreased up to six-fold within one generation.
'This is a previously unrealized challenge in cockroaches,' said Purdue University professorMichael Scharf.
'Cockroaches developing resistance to multiple classes of insecticides at once will makecontrolling these pests almost impossible with chemicals alone.'
The study published in the journal Scientific Reports focused on the species Blattellagermanica L, which can be found all around the world.
The team tested different insecticides from different classes, and combinations of the bunch, inmulti-unit buildings in Indiana and Illinois over a period of six months.
Exterminators often mix insecticides of different classes to ensure they're eliminating bugs thathave developed resistance to one, the authors note.
Roaches were captured from the sites before the lab to assess the best treatment for eachscenario.
'If you have the ability to test the roaches first and pick insecticide that has low resistance, that ups the odds,' Scharf said.
'But even then, we had trouble controlling populations.'
The team says it was able to keep the roach populations stable during the study period, butcould not make a significant dent in their numbers.
With the two-insecticide mixture, the pests even appeared to thrive.
One of the single-insecticide experiments suggested the population was at first vulnerableto the method, and in that case they were able to mostly wipe them out. But, in another trialwith 10 percent starting resistance, the population grew despite treatment.
Surviving roaches then led to more resistant offspring.
'We would see resistance increase four- or six-fold in just one generation,' Scharf said.
'We didn't have a clue that something like that could happen this fast.'
Female cockroaches can produce as many as 50 offspring during their three-monthreproductive cycle.
Even a small percentage of resistance and the potential for cross-resistance could mean acockroach population just keeps coming back.
'Some of these methods are more expensive than using only insecticides, but if thoseinsecticides aren't going to control or eliminate a population, you're just throwing moneyaway,' Scharf said.
'Combining several methods will be the most effective way to eliminate cockroaches.'
The American cockroach (Periplaneta americana) is an omnivorous scavenger and one of thelargest insect species that lives in close proximity to humans.
It has one of the largest genomes known to exist among insects, second only to the commonlocust.
In total, the species has 20,000 genes - which is the same number as a human.
Some genes control its internal detoxification system, which means the cockroach doesn'tget ill if it eats toxic food.
More genes help it combat infections, meaning it is resilient to living in filthy conditions.
Cockroaches can also regrow limbs thank to its remarkable genetic sequence.
Scientists have also found that female cockroaches are so resilient they don't need a malepartner.