An immensely long (7–8 mm) and slender (15 μm) ovipositor of the parasitic fig wasp Apocrypta westwoodi is equipped with a sharp, zinc-coated tip, ready to bore through the woody fruit, according to scientists Dr Namrata Gundiah and Lakshminath Kundanati from the Indian Institute of Science in Bangalore.
Parasitic fig wasp Apocrypta westwoodi on a fig. Photo credit: Lakshminath Kundanati.
The scientists were intrigued by the differences between the egg delivery systems of the boring parasitoid wasp Apocrypta westwoodi and the wasp that pollinates the fig’s flowers, Ceratosolen fusciceps.
“Our first question was what are the different adaptations that these two species undergo,” commented Dr Gundiah, who is the senior author of a paper published in the Journal of Experimental Biology.
They used scanning electron microscopy to take a high resolution look at the tips of the insects’ ovipositors and were amazed to see that the end of the boring wasp’s ovipositor looked like a drill bit, complete with teeth to bore through the woody fruit. In contrast, the tip of the pollinator wasp’s ovipositor closely resembled a spoon-like structure.
And, when they looked along the length of the borer’s ovipositor, they noticed tiny pits in the shaft, roughly in the location where the structure bends as the female drives the tip into the fruit to allow the ovipositor to flex without breaking.
They could also clearly see sensory structures at the tip that could help guide the ovipositor to the best locations for the wasp to lay her eggs.
Dr Gundiah and Kundanati then investigated the material from which the drill bit was made.
Focusing a beam of electrons on the minute tip, they recorded the X-ray spectra emitted by the material and discovered that the tooth structures were enriched with zinc.
“Zinc mainly increases the hardness, which will affect the wear resistance of the drill bits,” Dr Gundiah said.
Kundanati and Gundiah then prodded the minute drill bit with an atomic force microscope probe to indent it to measure how hard the zinc-enriched teeth were.
They recorded the hardness of the teeth at 0.5 GPa – that is almost as hard as the acrylic cement used for dental implants.
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Lakshminath Kundanati & Namrata Gundiah. 2014. Biomechanics of substrate boring by fig wasps. J Exp Biol 217, 1946-1954; doi: 10.1242/jeb.098228
