Weevil Evil: Betraying Symbiotic Partners Once They Aren't Needed

Weevils are pests that have a destructive appetite for grain crops, namely rice, wheat, and maize - crops that can be found at all major corners of the world. However, tearing through food supplies alone is not what makes them seem evil. It's what they do to their allies that makes you think, "that's one nasty bug."

It was first discovered that the cereal weevil had an unusual relationship with very specific gut bacteria back in the early 1930s. Under microscope, a curious bug-lover can see that young weevils boast special organs called bacteriomes that branch from their guts and ovaries like leaves on a tree. And packed inside each of these strange chambers are entire communities of bacteria belonging to a species called Sodalis pierantonius.

Symbiosis with gut bacteria alone is not unusual. Humans, for instance, can only resist some deadly infections thanks to the immensely varied microbial community that lives within their intestines. Nature World News even recently reported how a certain type of soil-dwelling bacteria may help improve human skin health.

However, the Weevil seems a particularly generous symbiosis partner, providing Sodalis its own chambers in which it is protected from the weevil immune system and left to thrive.

However, the rent for these little suites may be much more than the bacteria would like. When a weevil reaches full adulthood, the microbiomes found in its body suddenly disappear, the Sodalis vanishing with them.

Now, researchers led by Aurelien Vigneron at the University of Lyon in Villeurbanne, France, believe that they have determined what's really going on here, and it casts a dark shadow over the idea of symbiosis.

According to a study recently published in the journal Current Biology, the cereal weevil is more-so the captor and farmer of Sodalis than its partner. After close examination of the development of young weevils, Vigneron and his colleagues found that to develop its thick and strong adult shell, a weevil needs two amino acids - phenylalanine and tyrosine - that are just not abundant enough in the grains that the pest traditionally eats. However, it turns out that Sodalis is particularly good at producing these two acids, essentially supplementing the weevil's inadequate diet.

And what do these bacteria colonies get for all their hard work? A slow death via digestion. According to the researchers, once a weevil fully matures with a strong shell, it no longer needs its microbiomes, and unceremoniously closes these sanctuaries for good. The bacteria trapped inside are quickly dissolved and converted into energy to help the weevil start its new adult life.

So what is nature trying to tell us here? It's the same message that horror films have been telling us for years: If the price of that house seems too good to be true, it probably is.