Beetles Have A Clever Way to Keep Symbiotes Safe During Their Metamorphic Contortions

Just as we do, insects have friendly microbes that help them stay healthy.

Insects undergo extreme body warping to metamorphosize into their older stages of life instead of simply growing larger.

These life-changing contortions make it difficult for the microbes to live.

The convoluted process can completely distort and shift organs and other tissues, so any microbes along for the journey would not be in for a survivable ride.

Rebekka Janke from Johannes Gutenberg University of Mainz and colleagues took a close look at the process of transformation in the darkling beetle.

Darkling beetles rely on Burkholderiabacteria for success in reproduction.

The beetles' eggs are vulnerable to infections, but they keep their offspring safe by producing polyketide chemicals that have anti-bacterial properties.

One particular strain of the beetle, B. gladioli, or Lv-StB, has become so accustomed to living within the beetle that it has lost all ability to move.

Janke and the team used fluorescent markers, microCT scans, and a sample of thebacteria's DNA to track what happened to the microbe.

After the mother beetles coat their eggs with saliva, the bugs are exposed to the surface of the eggs for six days.

Once the baby beetle grubs hatch, the bacteria gather into three deep lower back folds. The symbiotes are protected by these folds, but they also contain glandular cells that help nourish thebacteria.

The pockets get wrinkled during the transformation. They allow some of thebacteria to escape onto the surface, this time onto the pupae, ready to move towards the adult beetles' reproductive organs.

The researchers did not find any B. gladioli in the pupae guts.

Researchers put fluorescent beads on the developing pups. When the beetles emerged as adults, most of the beads ended up in their back pockets.

Laura Flrez of the University of Copenhagen says that Lagria beetles modify their pockets on their backs in order to keep their symbionts.

Most of the process of entering the adult glands is done in female beetles. Male adults lack symbiotes and their back pockets are smaller than that of females.

The main purpose of the symbiotic organs is to allow successful transmission onto the egg stage and to the next generation. Male adults don't need to carry symbionts since only females lay eggs.

An example of how solitary insects avoid this potential loss is provided by the new results of the study.

According to Janke and her colleagues, the importance of the symbionts likely drove the evolution of specialized structures in the host to house and maintain thebacteria.

It was published in a journal.