To survive, cockroaches reject sweets

Scientists find a neurological mechanism that creates an version to glucose used in baits to kill insects - One of the oldest ways to get rid of cockroaches was always to mix a sweet food (glucose is preferred) with poison in a bait. But at the end of the 1980s, something went wrong with this strategy in a flat test in Florida.

One popular brand of bait stopped working suddenly. The populations of cockroaches in the apartment began to increase. Confused, the researchers began testing theory after theory until they found the explanation:

In a demonstration of evolution, many cockroaches have lost their taste for sweet foods, rejecting the corn syrup used in bait.

In five years, the rejection of the sweet taste has become so common that the trap was considered useless.

"Cockroaches are very adaptable and are doing well in the war versus humans," said entomologist at North Carolina State University, Jules Silverman, who discovered the aversion to glucose in Florida over two decades ago.

This discovery illustrated the evolutionary ability that created the fame of cockroaches can survive even a nuclear war.

In a study published this week by the journal Science, Silverman and other researchers explain the operation of the genetic mutation that gave them a competitive advantage that allowed them to survive and multiply.

The key is in some neurons that signal the brain about certain foods.

Normally,  glucose activates certain neurons that like sweet food. In bugs with the mutation, glucose activates both sweet neurons, but also other neurons, which reject the glucose and overlap the signal of the first - so the brain gets the message that the sweet taste is bad. This unusual neurological activity appeared in cockroaches that dislike glucose collected in Puerto Rico and descendants of the cockroaches from Florida.

The research focused on the German cockroach, a small species that can even take a ride in shopping bags, but not the biggest cockroaches known as American cockroaches. The aversion to sweet was also found in small cockroaches in Southern California, Cincinnati, Indiana, South Korea and Russia.

Now, scientists are trying to discover whether other types of cockroaches also have these peculiar eating habits.

But does the study explain why it is so difficult to get rid of cockroaches at home?

Probably not, says Coby Schal, study co-author who also works at North Carolina State.

Tests show that cockroaches averse to glucose eat most of the current baits, suggesting that the manufacturers withdrew or mask these ingredients. (The exact ingredients of insecticides are industrial secrets). Moreover, scholars have found that aversion in only seven of 19 populations surveyed in different places.

According Schal, if the bait purchased is not working, the most likely explanation is incorrect usage.

Still, the researcher explains, the new work has the potential to help consumers. By studying how the cockroaches evolve to escape our poisons, scientists can find clues to create baits that insects cannot resist.

It is unclear when the Florida cockroaches found the baits with glucose and how quickly they abandoned the taste for sugar. But Schal explains that it is reasonable to estimate that this feature needed five years to spread among many to end the effectiveness of the product. That means it took 25 generations of German cockroaches, which are reproduced from a month old one.

The aversion to glucose may have been an individual in response to the bait, or already be present in some insects, and when the bait appeared, it gave them an evolutionary advantage. Their offspring inherited the gene and gradually began to replace other cockroaches.

The Purdue University entomologist Michael Scharf, who studies urban pests but which was not involved in the new study, noted that since the 1950s, studies show that cockroaches have also developed resistance to insecticides and agreed that this discovery may help in developing best products to control insects.


Translated from the Portuguese version by:

Lisa Karpova
Pravda.Ru