SHARPE almost impossible to kill, practically invincible. A new study – which will not please those who are afraid of cockroaches – tells how some of these insects are becoming more and more resistant, so much so that insecticides and other products seem to have no effect on them anymore. The rise of some cockroaches (Blatella germanica) was recently reported in a research by Purdue University published in the journal Scientific Reports.
The researchers explain how within a single generation these cockroaches have been able to evolve to respond to the effects of sprays, pesticides, insecticides and other remedies to eradicate them: in practice they can even resist new chemicals to which they have never been exposed before.
“We had no idea that something like this could happen so quickly,” says lead author Michael Scharf of the Entomology Department at Purdue University. The scientist says that in just one new generation these animals are able to increase resistance four or even six times over the previous generation.
In order to discover the adaptation of these insects, experts carried out tests using three insecticides (abamectin, boric acid and thiamethoxam) inside some apartments in Indiana and Illinois infested with cockroaches. In a first treatment, three different insecticides were used every month for three months. In a second, two different insecticides were used for six months and in the third test one insecticide was chosen to which the cockroaches had low initial resistance.
No chemical cocktail, regardless of duration or rotation, was able to eradicate the cockroaches or even reduce their populations. Even, with the use of a single insecticide, the number of insects increased by 10%, thanks to an increase in resistance. With the use of two products in the first six months of the year the populations increased and in the third case, when three insecticides were used, the number of insects remained the same. The same tests were then replicated in the laboratory confirming that the offspring of the cockroaches proved “substantially immune” to the remedies used.
These results are worrying when you think that the cockroaches are able, in a reproductive cycle of only three months, to give birth to as many as 50 insects at a time. Part of the offspring develops greater resistance and gives rise to a cycle of “invincible” insects that can carry bacteria, salmonella, allergens and other risks to human health.
A new challenge is therefore necessary for scholars, made up of combinations of chemical treatments, traps, improved toilets, special vacuum cleaners and other strategies to try to defeat the presence of cockroaches: one insecticide in many cases is no longer enough.
“Cockroaches that develop resistance to several classes of insecticides at once make the control of these pests almost impossible only with chemicals – concludes the author of the study – we should prepare ourselves to combine different and new methods to defeat them”.