How the Beetle Gets Its Shell

Even in an age of Gore-Tex and other high-tech wearable fibers, there may be no better coat for withstanding the elements and protecting a body than that belonging to an insect.

Durable, yet flexible and lightweight, the sturdy shell encasing most insects has undoubtedly helped ensure their evolutionary success and great abundance. And now, scientists with the Agricultural Research Service (ARS) and their colleagues have discovered which of a beetle's genes are responsible for crafting this impressive coat.

Richard Beeman, an entomologist in ARS' Grain Marketing and Production Research Center in Manhattan, Kan.--with help from retired ARS researcher Karl Kramer and researchers at nearby Kansas State University--learned that just three genes orchestrate the complex process.

One gene cues production of the beetle's outer cuticle, called the exoskeleton, while another prompts an enzyme to start building the cuticle that lines the insect's gut. A third finishes the job, telling the fresh outer skeleton to harden into a protective armor, guarding the insect against injury, infection and desiccation.

The findings, some of which were published in a recent issue of the Proceedings of the National Academy of Sciences, could spur development of new, nonchemical forms of insect pest control.

To serve as their model, the researchers chose a well-studied insect, the red flour beetle (Tribolium castaneum). This rust-colored beetle is known in the grain industry for its costly invasions of stored cereals and nuts.

Beeman had already amassed extensive genetic information about the insect. His genetic maps of the beetle and other colleagues' findings, in combination with recently released genome sequencing information, laid the necessary groundwork for the recent study.

Using a technique called RNA interference, the researchers "knocked out" certain candidate genes to determine which were involved in synthesizing the chitinous material that makes up insect shells.

They knew they'd identified one of the key genes when, after deactivating it, the cuticle in the research beetles stayed white and soft. It didn't tan and harden the way it normally would.

ARS is the U.S. Department of Agriculture's chief scientific research agency.