Cockroaches hate sugary sweets


Cockroaches hate sugary sweets, according to a new study published in the journal Science. That is, some species of cockroaches hate sugary sweets, anyway, like the German one. It is the smaller cousin of the larger ones more commonly found in America.

The German cockroaches are slender, small, and brown and live all over the world in homes, offices and apartment buildings. They are one of the species that has evolved to avoid the taste of glucose. They have evolved to consider the taste of glucose to be something to avoid, as it has been an ingredient in some cockroach traps used to eradicate them.

Glucose, according to scientists, sets off bitter taste receptors for some species of roaches. This, in turn,  causes them to avoid food that causes this reaction and to avoid the traps containing glucose. The gene that causes the roaches to avoid glucose is passed down to their offspring and, as a result, more cockroaches are being born that avoid glucose-filled traps.

Tests were conducted by scientists on the tongues of roaches to examine the reactions that sugar has on them. While it’s become common knowledge that cockroaches and other insects become resistant to the poison, or pesticide, over time, this study revealed a something new. Rather than the roaches avoiding the poison, they were, instead, avoiding the sugar.

The scientists were able to determine that the taste of sugar in some roach traps sets off the bitter reaction in the roaches, causing them to avoid the glucose.

North Carolina State University entomologist Jules Silverman was the  discoverer of the glucose aversion in that Florida kitchen during a bait test. According to her, “Cockroaches are highly adaptive.”

Coby Schal, another entomologist at North Carolina State University and one of the study’s authors, stated that when prehistoric roaches lived in the wild they were glucose-averse. That means they were likely to avoid toxic glucose found in certain plants. When humans began combining glucose with poison to create roach bait, they could have restarted that ancient reaction.

In his study, Schal  states: “Most times, genetic changes, or mutations, cause the loss of function. In this case, the mutation resulted in the gain of a new function – triggering bitter receptors when glucose is introduced. This gives the cockroach a new behavior which is incredibly adaptive. These roaches just got ahead of us in the arms race.”

The scientists also captured video of the roaches entirely avoiding a mound of jam containing glucose and flocking instead to a glob of peanut butter.

“We are showing that cockroaches can learn incredibly well. They can associate the punishment of tasting glucose with the smell of the bait,” Schal stated.

The scientists found seven out of the nineteen populations of cockroaches that they studied contained glucose-averse roaches. The tendency of some cockroaches to avoid traps that used glucose was first observed in the early 1990’s, about seven or eight years after commercial traps using glucose came on the market and entered into widespread use, said researcher Coby Schal of North Carolina State University.

Scientists, in order to prove this theory, plan to examine changes in cockroaches’ DNA over time. Schal’s team has roaches from the 1930s to present day preserved in a fridge, and they will use them to conduct further research on this theory over the next five to ten years.

“We haven’t used any kind of trap that used sugar for years,” states Bob Kunst, president of Fischer Environmental, a pest control company in Louisiana.

Kunst was not involved in the study. He described German cockroaches as being “filthy little creatures” because they can carry salmonella.

Do not despair, though, if you have a roach infestation and want to get rid of the pests. Though some roach species have evolved to avoid glucose, they still seem quite happy to consume fructose.

Some bait manufacturers, like Kunst, have already made  the few small adjustments needed to ensure that the baits they sell will be successful at   eradicating roaches, and others are following suit. Like the cockroaches, in a manner of speaking, the bait manufacturers need to evolve to survive.


Written by: Douglas Cobb

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