What causes the cockroach odor

Insect researchThe scent of the cockroaches

A cockroach rarely comes alone. Roaches love company, as Coby Scarf knows:

"They absolutely do. They love company of their own species - not so much us."

They like to be in the company of their own kind, not of us humans, explains the entomologist from North Carolina State University in Raleigh. But because the German cockroach can be found almost exclusively in human dwellings, it mainly leaves its shelter at night - and thus avoids people. This way of life poses special challenges in how it orientates itself and finds its way to its fellow cockroaches.

"At night, the most effective method of communicating with the help of chemicals. Because the view is a little restricted in a dark kitchen cupboard. This is why cockroaches have a keen sense of smell. They can literally smell their fellows - based on the smell of faeces Chemicals in the feces. They secrete it in the places where they sleep during the day.

Bacteria as accomplices

These scents and attractants are called aggregation pheromones that bring cockroaches together regardless of their gender. There is no shortage of publications on the chemical nature of substances. On the contrary, the studies seem to contradict one another, as the potential pheromones often differ from cockroach colony to cockroach colony. And that gave Coby Schal the idea that it is not the insects themselves that produce the attractants, but bacteria in their digestive tract.

"To check this, we raised the insects under sterile conditions. We made the eggs of cockroaches aseptic and then let the animals grow up from them. We found very few substances in their droppings that could be used as attractants. We have extracted these chemicals and tested how other cockroaches react to them. They weren't exactly attracted to these extracts. "

40 different fragrance messages

However, if the entomologist inoculated the sterile insects with the intestinal bacteria that normally occur in them, the wallflowers turned into attractive members of the colony. The fragrances are volatile carboxylic acids, i.e. organic acids. Forty different of these are usually produced by the bacteria in the cockroach's intestines. Coby Schal suspects that just a few substances from this class of substances are sufficient to attract the cockroaches. Exactly which these are could vary from colony to colony. Even if the researcher from North Carolina emphasizes that his investigations are basic research, he can still easily imagine applications in pest control.

"All substances that cause cockroaches to congregate in one place come into consideration. Because that is precisely what it is all about: that the insects gather where we can eliminate them. If we could prepare traps with these carboxylic acids , that would be useful.