If you complimented a woman Lagria beetle on the pupa’s shell, she would probably reply, “Thank you, it has pockets!”
These special pockets contain an important treasure: symbiotic bacteria which protect the pupa (and the larva that precedes this stage) from a potentially lethal fungus. When the adult beetle emerges from the pupa, the friction from metamorphosis pushes the bacteria out of these pockets into the beetle’s abdominal glands.
Although scientists knew about pockets and bacteria (primarily a strain of bacteria called Burkholderia), inhabiting the abdominal glands of beetles of the genus Lagria, it was not known how they were related, or how the bacteria ended up in the abdomens of the beetles in the first place. Recently, a team of researchers identified the missing steps in this symbiotic relationship by observing what happens when an adult beetle emerges from a chrysalis by scanning the pupa and creating 3D digital models. The new study was published Tuesday (August 30) in the journal Frontiers of physiology (will open in a new tab).
“Mushrooms are indeed the main natural enemies of most insects, so they are a threat, especially if [the insects] live in fallen leaves Lagria Beetles do this, study co-author Laura Victoria Flores Patino, a biologist and researcher at the University of Copenhagen in Denmark, told Live Science. Therefore, it is important to understand how these beetles can retain protective bacteria throughout the life cycle of insects, the study says.
Connected: This beetle can walk upside down on the bottom of a puddle of water (video)
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Lagria The genus includes about 800 species of beetles distributed throughout the world. Only adult female beetles carry symbiotic bacteria that release chemicals that are poisonous to the fungus. In adult beetles, bacteria live in special glands near the oviducts of insects, from where the eggs are released. When the beetle lays eggs, the bacteria settle on the surface of the eggs; the bacteria move on to their new beetle hosts when the eggs hatch and stay with them into adulthood.
But Lagria beetles experience some extreme changes in their lives. They emerge from eggs as worm-like larvae and then grow into immobile ovoid pupae. Inside the chrysalis, beetle larvae “get rid of a lot of what they have inside.” [their bodies] and restore,” Flores said. At the end of the pupal stage, adult beetles emerge fully formed.
So how does the bacteria stay with the beetle during these major life changes?
To answer this question, the researchers coated newly pupating beetles with tiny fluorescent plastic beads only 1 micron thick. (For comparison, a human hair is between 17 and 180 microns thick.) After the beetles emerged from their pupae, all the balls—substitutes for symbiotic bacteria—gathered at the tip of the beetle’s abdomen. The researchers suspected that the beetle’s friction against the pupal shell as it emerged pushed the bacteria toward the abdomen. Once the bacteria were in their new home on the bodies of the beetles, they were ready to be carried over to the next generation of beetles. Lagria beetles.
But where did these beneficial bacteria come from? When you think of symbiotic bacteria, bacteria in your gutor in the digestive system other animals, may come to mind. Flores suggested that Lagria beetles have developed an external symbiotic relationship with these bacteria because of all the changes that take place inside the pupa. “If you’re a symbiont that’s inside and highly integrated, you can get lost,” as the beetle larva breaks down and rebuilds its entire body, Flores explained.
Lagria beetles are not the only insects to have developed this adaptation. Leaf-cutting ants also carry symbiotic bacteria in exoskeleton pockets, Flores said, and there is a species of weevil that carries yeast in special pockets.
While this new study sheds light on how bacteria get from the pupal pockets into the beetle’s abdomen, the study’s authors have a few more questions, Flores said. For example, further research could show how bacteria actually get inside beetle glands, how bacteria protect beetles from fungi, and whether bacteria provide protection from predatory animals.
Originally published on Live Science.