Cockroaches are becoming increasingly stronger and, soon, killing them with insecticides may be nearly impossible. This is not a horror movie script, but the conclusion of a research conducted by Purdue University. The work shows that the evolution process of the German roach species (Blattella germanica L.) is making the insect, rapidly and efficiently, more resistant to the strongest class of chemical products.

“Cockroaches developing resistance to multiple classes of insecticides at once will make controlling these pests almost impossible with chemicals alone,” said study leader Michael Scharf in a statement to the University. He also said that the problem is bigger in urban areas with low income housing.

See also:
Have you heard of cockroach bread?

Fumigation processes normally mix multiple classes of insecticides to eliminate varying types of cockroaches and other insects – if a species is resistant to a specific poison, there is another one in the same mix that can kill it. By using this technique, Scharf and his team tested three insecticide formulas of different classes during six months inside buildings in Indiana and Illinois. Later, they followed this procedure twice: first, with two combinations of insecticides and then with one alone.

After the roach extermination stage, scientists cross-checked information from insects collected before the study and those surviving the event. Then, they identified German roach populations that remained stable in the first stage of the work, but actually increased in the second stage. 

The conclusion was that cross-resistance was vital for the species survival. This means that roaches surviving a specific type of pesticide mated roaches resistant to other type of pesticide and all their line of descendants became immune to both pesticides thereafter.

And the problem is even bigger because the roach reproduction cycle is extremely fast: it lasts three months and may generate up to 50 descendants. “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.”

Barata germânica ou alemã (Blattella germanica L.) é conhecida também como barata de cozinha. Crédito: Wikimedia Commons

What can we do about cockroaches?

Cockroaches pose a series of risks to human health. In their body, they carry hundreds of types of bacteria harmful to humans, as E. coli and salmonella. Additionally, their organic debris, such as saliva, feces and body parts, may lead to severe allergies, especially in children. 

Without efficient insecticides, how can we tackle their population growth? To Scharf and his peers at Purdue University, we should combine chemical treatments and mechanical traps, aspirators and improvements in urban sanitation.

“Some of these methods are more expensive than using only insecticides, but if those insecticides aren’t going to control or eliminate a population, you’re just throwing money away,” Scharf said. “Combining several methods will be the most effective way to eliminate cockroaches”, he added.

Content published in July 24, 2019