The Cockroach Communication Network


New research indicates cockroach communication is dependent on microbes in their feces. (Photo credit: Erik Karits/Shutterstock)

Chances are, you’ve seen a gathering of cockroaches some place at some time. Conditions don’t even need to be especially filthy for these most reviled of insect pests to appear.

Even potentially more disgusting is that, even if you only see one of them, you can be pretty certain that others aren’t far behind, as the cockroach tends to be one of the more socially connected bugs on the planet. While scientists always suspected that the cockroach emitted some kind of pheromone that alerted others of its kind to its position, recent research now has suggested an interesting source for this chemical indicator. The cockroach literally has its own insect internet constructed from the microbes in its feces.

In the past, scientists accepted that feces played a role in the cockroaches’ aggregating behavior. However, debate over the origin of the most significant compounds comprising the pheromones ranged from substances on the bug’s skin to nitrogen-rich compounds in the feces or even fatty acids. The confusion prompted North Carolina State University entomologist Coby Schal to wonder if perhaps the conflicting results indicated that the roaches used different aggregation chemicals depending on their environment, the food they ingested, or the microbes they carried in their stomachs. To test the theory, he sanitized a group of German cockroaches, Blattella germanica, and raised them in germ-free cages. No germs in the environment meant no germs in their feces. As he suspected, the sterilely raised cockroaches did not share the same amount of social interaction as their germ-laden counterparts. What is more, when those cockroaches raised in the sterile environment were once again fed normal feces, the aggregating behavior reappeared.

The next step was to do what every entomologist dreams of doing: analyze the two feces to see what exactly was different about each. They identified 40 different chemical compounds in the feces of the normal cockroaches, while the sterilely raised ones lacked 12 of these altogether and had only minuscule amounts of 24 of the others. The most significant of these compounds appears to be a collection of volatile fatty acids that tend to quickly evaporate from normal feces and so would seem to comprise the “scent” others detect. As lead author of the study Ayako Wada-Katsumata explained, “The chemical compounds seem especially essential for nymphs (i.e., young cockroaches). It’s important for nymphs to determine a safe place, and these pheromones help do just that.”

The study also makes clear why previously there hadn’t emerged a consensus over the exact origin of the pheromone. As Schal suggests, the results show that “aggregation is plastic, as compounds can be mixed and matched for different groups of roaches, depending on their environment.” Essentially, the microbes in different groups of cockroaches essentially “cook up” a distinct “aroma” for that group, one that is directly influenced by the environment and one that other members of the group can use to locate others of their own kind. The next step for the North Carolina State team is to determine exactly how targeted these different mixtures can get.

For science, perhaps the most significant aspect of the study lies in what it suggests about the importance of microbes in insect-to-insect communication and perhaps in higher organisms as well. For the consumer hoping to maintain a bug-free home, or for those freaked out by the pests in general, it may lead to better methods for controlling infestations. It also would appear to underscore why getting rid of these nuisances hasn’t been as easy as it would appear to be. They have had millions of years to perfect their cockroach communication system.

More to Explore
Cockroaches communicate via bacteria in their feces
Gut Bacteria Important Factor in Cockroach Gathering
Cockroach swarming pheromones produced by gut bacteria
Gut bacteria mediate aggregation in the German cockroach [abstract]

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