We know a little more about the metamorphosis of insects!

Just like humans, insects live in symbiosis with microbes, helping them to maintain good health. During their evolution, they must pass through major body transformations. During these metamorphoses, organs and other tissues can be completely deformed and displaced. So friendly microbes have a hard time surviving in these conditions.

A beetle

Evolutionary ecologist Rebekka Janke of Johannes Gutenberg University Mainz and her colleagues conducted a study to find out what happens to these microbiota. They analyzed this transformation process in the mealworm Lagria villosa.

A real battlefield between microbes

The researchers were able to track what happened to the microbes using fluorescent markers, microCT scans and a DNA sample from the bacteria. They discovered that the mealworm depended mainly on the bacterium Burkholderia for successful reproduction. This bacterium protects their offspring by producing chemical polyketides with antimicrobial properties.

It is through glands near the ovaries that the female exudes Burkholderia onto the eggs. The microbes remain on their surface for about 6 days, fighting off parasites and hungry fungi. When the eggs hatch, the bacteria take refuge in three deep folds of the outer cuticle of the larva. These pouches protect and feed them through secretions from glandular cells.

A particular strain of Burkholderia, B. gladioli or Lv-StB, depends on the beetle for its survival. She’s gotten so used to living inside him that her ability to move has almost completely disappeared.

Male adult beetles lack symbionts

The intestines of nymphs do not have B. gladioli, so they do not pass through the internal route. Nevertheless, the researchers put polystyrene fluorescent beads the size of a symbiont on the developing pupae. They then discovered many at the end of the abdomen of adult mealworms. According to evolutionary ecologist Laura Flórez, these beetles were able to preserve these microbes during metamorphosis by modifying their unique back pockets.

The final step leading the bacteria to the adult glands is still a mystery. This process only occurs in female beetles since they lay eggs. Males begin to shed bacteria as early as the pupal stage, as they have smaller and narrower back pockets. Adult males are deprived of symbionts.


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