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Patrick Guilfoile: How to drill into a fig

Spoiler alert — fig lovers should be aware that reading this article may alter their inclination to eat figs. Proceed with caution.

Figs have a several interesting relationships with wasps.

One type of wasp pollinates the fig; in the process, female wasps lose their wings and antenna as they navigate the narrow opening into the fig.

The wasps end up dying inside the fig once they finish pollination.

Although they are ultimately digested by the fig, there is a bit of wasp in every fig you eat. (Do be aware, though that many foods have insect parts in them — a little extra protein for our diets.)

Another relationship that figs have with other wasps is more nefarious.

Parasitic wasps lay their eggs in the figs, but don’t help the plant out in the process.

Rather they inject their eggs through the outer skin of the fig, often into the larvae of a different type of wasp that is living inside.

How they do this had been a real mystery.

The wasps have a threadlike tool for injecting the eggs, called an ovipositor.

The ovipositor is about 1/3 of an inch long, and only 0.0006 inches wide, about 1/10th the thickness of a human hair.

Imagine trying to push a very thin human hair through the skin of a fig, and you can see the challenge.

Researchers at the Indian Institute of Science in Bangalore, India investigated the properties of the ovipositor that made this feat possible.

Electron microscopy was one of the key tools they used in their analysis.

This allowed very high magnifications and showed that these wasps had a tooth-like structure at the tip of the egg-laying ovipositor.

Using a special detector in the electron microscope, they also determined that the ovipositor was tipped with zinc.

Presumably, having some metal at the end of this egg-laying device makes it easier to drill into the fig.

These scientists identified several other features that helped the wasp penetrate the right fig.

One feature was sensory structures that detect scents associated with the appropriate figs and prey.

Another was a sensory structure could detect stress on the long appendage as it was pressed into the fig.

In addition, the scientists described a “bend not break” characteristic of the long ovipositor.

This structure is both flexible and tough, allowing it to be pushed deep into a fig, in order to find a tasty larvae for the wasp’s offspring.

So, the next time you eat a fig, thank a wasp for the treat, and imagine the battles that go on between different wasps, in and on a fig.

More information is available in: Lakshminath Kundanati & Namrata Gundiah. 2014. Biomechanics of substrate boring by fig wasps. J Exp Biol 217, 1946-1954; doi: 10.1242/jeb.098228

PATRICK GUILFOILE has a doctorate in bacteriology and is the associate vice president at Bemidji State University.