Young, developing beetles in their pupal stage look limp and mostly lifeless, except for maybe the occasional squirm. They’re somewhere between the grubby larva phase and the fully-matured adult stage. And while they’re obviously alive and breathing, researchers aren’t sure how pupae actually deliver oxygen to their tissues. Large adult beetles flex their abdomens like belly dancers, Science describes, to pump out carbon dioxide and push oxygen to the rest of their cells. As it turns out, so do their pupae, according to findings published in Biology Letters last week.
The spread, or diffusion, of gases within the trachea and its various tubular branches was thought to be sufficient to support metabolism in small insects. But this passive process isn’t enough for larger, more active bugs. These require active ventilation produced by abdominal pumping: parts of their tracheal system are rhythmically compressed to generate flow. This, however, has never been investigated in pupae. Developing insects in this stage are immobile, their metabolic rates are considerably lower, and their demand for oxygen is reduced. Presumably they don’t require this sort of active ventilation.
Virginia Tech’s Hodjat Pendar and colleagues used high-powered X-ray imaging at the Argonne National Laboratory to study the inner workings of Zophobas morio beetle pupae (pictured above) as they breathed. The team also measured their carbon dioxide emission, abdominal movement, and hemolymph pressure (their version of blood pressure).
The developing beetles, they discovered, periodically squeeze their tracheal system, collapsing their breathing tubes and producing a wiggle of the abdomen. This abdominal pumping also raises their hemolymph pressure and leads to carbon dioxide release – both associated with breathing.
However, more than 63% of these abdominal pumping events happened without any tracheal collapse and ventilation. This means that respiration isn’t the major function of the abdominal pump. They conclude that it likely serves other roles, such as internal gas mixing, reduction of water loss, or hemolymph circulation.
Here’s a cool video from Science: