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In order for a female parasitic fig wasp to successfully lay her eggs, she has to penetrate an unripe fig’s tough skin. Good thing she has what is essentially a power tool. A new study has discovered that the ultra-thin tool used for boring holes and injecting wasp eggs has a tip made of zinc.
A mechanical engineer, Namrata Gundiah, was the leader of the study done at the Indian Institute of Science in Bangalore, India. The fact that the structure is maneuverable yet hard makes it a challenging tool for drilling. Gundiah said that the structure is beautiful, efficient and makes an amazing system for boring holes.
Published in the Journal of Experimental Biology on May 28, the study has shown, for the first time, that the wasp drill bits are made harder by the zinc. Gundiah became intrigued by the parasitic fig wasp upon seeing them in a documentary by David Attenborough. She knew already that they used ovipositors, the long structures at their rears, for injecting their eggs into unripe figs. When the eggs hatch, the new wasps exploit the other larvae that are growing inside the fig.
With Lakshminath Kundanati, one of her graduate students, Gundiah pondered how the wasp’s ovipositor tips were tough enough for drilling into the skin of the young figs. They were also curious about whether the tips of the ovipositors belonging to parasitic wasps (Apocrypta westwoodi grandi) were any different structurally from the ones on the (Ceratosolen fusciceps) pollinator wasps. That species of wasp lays eggs in the soft flowers of the fig tree.
From the fig trees on campus, the researchers got some subjects of both species to study. They collected some more from a more wild environment as well. In order to take high-resolution peeks at the ovipositor tips, they used electron microscopes. Indeed, the pollinator wasp had a spoon-shaped tip. Conversely, the parasitic wasp tip resembled a drill bit, complete with indentations that were decidedly teeth-like.
With an x-ray detector and the electron microscope, they discovered the presence of zinc. It was only on the tips of the parasitic fig wasp’s ovipositors. Gundiah said, “We see it very consistently only at the tip and not anywhere else.” By utilizing atomic force microscopy, she was able to determine that the tips enriched with zinc were as hard as dentist acrylic cement.
Another of the researchers’ queries was how the slender ovipositors could operate without ever breaking. What Gundiah and Kundanati found, upon filming the creatures as they bored into unripe figs, was that the ovipositor was flexible. It would bend, but the ovipositor would not break. Gundiah called it a very clever design.
Making these discoveries about the parasitic fig wasp has been an inspiration to Gundiah. She believes that the wasp’s zinc-tipped drill bit could easily serve as a foundation for improving microscopic boring needles, probes and tools. The design could be particularly helpful for surgeries that need to be minimally invasive. Gundiah has studied steel and various synthetic materials. She said that when the same ideas are applied to biological systems, new possibilities are opened to understanding the workings of nature.
By Stacy Lamy