Surprisingly, cockroaches are steering away from sugary-coated traps designed to kill them. The phenomenon has been subject to much scientific interest with many experts asking why they avoid the traps if they are coated in glucose – a tempting treat for cockroaches.
A new study published in the May 24th edition of Science has revealed why.
Cockroaches determine whether or not food is safe by using their sensory systems. However, these sensory systems are able to quickly adapt to environmental changes.
How they are able to detect the presence of poison in food that was once considered to be “safe” – according to their sensory systems – is still a mystery.
Researchers at North Carolina State University looked at a species of cockroaches that have adapted and avoided traps coated in sugar, they were able to determine the mechanism of this change.
Cockroaches have tiny little hair-like sensors on their mouths which they use to “taste” food, activating sensors house gustatory receptor neurons, or GRNs. Certain GRNs activate in the presence of food that is sugary – which makes them feed – as opposed to GRNs that activate in the presence of food that is bitter – making the animal avoid the food.
The research, which started in the mid-1980s, found that German cockroaches given baits incorporating a stimulant (glucose) and a deterrent (insecticide) evolved a behavioral change called “glucose aversion”.
Cockroaches with “glucose aversion” avoided all man-made traps even though they were coated with glucose.
Using electrophysiological tests the scientists were able to analyze the responses of gustatory receptor neurons among normal and glucose averse cockroaches.
They were surprised to find that when the German glucose averse cockroaches were exposed to sugar it actually stimulated their bitter GRNs and suppressed the sugar GRN response, which prevented them from feeding.
This means that among glucose-averse German cockroaches glucose is processed as a deterrent which makes them avoid it completely.
The finding highlights the the plasticity of the cockroach sensory system.
Corresponding author Coby Schal, the Blanton J. Whitmire Distinguished Professor of Entomology at North Carolina State, said:
“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.”
Schal noted that it is also possible that the environmental adaptation could have started millions of years ago – before humans were around – when they avoided some plants that are capable of producing toxic, but sweet, compounds.
He said that the pest control industry needs to consistently vary the type of baits in order to always be one step ahead of the cockroache’s ability to adapt.
It’s especially important to find efficient ways of controlling cockroach infestations, the National Pest Management Association (NPMA) recently reminded families that cockroach allergens can cause allergies and asthma attacks. The saliva, droppings and decomposing bodies of cockroaches contain allergen proteins known to trigger allergies and increase the severity of asthma symptoms, especially in children.
Written by Joseph Nordqvist