During metamorphosis, beetle pupae are hidden in the pockets of their symbiont bacteria

(ORDO NEWS) — Scientists have discovered special pockets in female beetle pupae from the genus Lagria, in which they hide symbiotic bacteria during the transformation from larva to adult.

During the final transformation of the bacteria, by rubbing the beetle’s body against the cocoon, the pupae are transferred to glands located near the female’s genitals, from where they can be transferred to offspring.

Beetles of the genus Lagria require symbiotic bacteria at all stages of immature life. However, during this period, insects go through a series of metamorphoses, turning from an egg into a larva, and from a larva into a pupa.

Their body is undergoing a massive reorganization, so bacteria can’t stay in the same place all the time.

Now scientists from the University of Copenhagen (Denmark) have figured out how insects solve this problem.

It turned out that cockuli of Lagria females have special pockets on their backs, which allow them to protect symbionts during metamorphosis and facilitate their movement after pupation to the organs of adults.

The females of many Lagria species carry a mixture of beneficial bacteria in their glands next to the oviduct.

When they lay eggs, the bacteria are “squeezed” out of the glands and deposited on the surface of the eggs. Substances that produce these symbionts protect eggs, larvae and pupae of beetles from fungi.

Moreover, some of these bacteria are not able to survive outside the body of the beetle – for example, the main representative of the microbiota L. villosa , a strain of the bacterium Burkholderia.

Scientists scanned pupae of two species – Lagria villosa and Lagria hirta – using microcomputed tomography and found three unique two-lobed pockets at the end of the thoracic segment of female pupae.

Similar structures in these species of insects were not previously known. In male pupae, pockets are rudimentary and contain either few or no symbionts.

At the adult stage, symbiotic bacteria do not perform a protective function, but only must be passed on to offspring, so males do not need symbionts, because females have to lay eggs.

To find out how the bacteria move from the pupal pockets and glands in the adult genitalia, the scientists scattered many polystyrene fluorescent beads about a micrometer wide on the surface of early pupae.

After development and emergence from the pupa of an adult insect, most of the balls ended up at the tip of the beetle’s abdomen – just where the genitals are located.

The authors believe that the balls, and presumably symbionts, are moved to the genitals by friction during the hatching process.

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