Zinc-hardened Drill Bits Allow Parasitic Fig Wasps to Bore Holes to Lay Eggs
One of the main goals in the life of a female insect is to find the best place to lay her eggs. For one particular fig wasp (Apocryta westwoodi grandi), this involves boring through a tough, unripened fig with her immensely long ovipositor in order to find the larvae of other insects that are already developing within, which she then parasitizes to give her own eggs the best start in life.
Namrata Gundiah, from the Indian Institute of Science, was intrigued by this egg-delivery system and wondered how the wasp’s ovipositor, which is 7-8 millimeters long, could bore through the woody fruit. Using scanning electron microscopy and an atomic force microscope probe, she found that these tiny fig wasps are equipped with a zinc-tipped drill bit. Her research was recently published in the Journal of Experimental Biology.
The following video shows the Apocryta westwoodi as it bores into a fig with its extra-long ovipositor. SPOILER ALERT: There’s a really cool surprise ending!
Teaming up with graduate student Laksminath Kundanati, Gundiah used scanning electron microscopy to take a high resolution look at the tips of the insects’ ovipositors and was 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. When they looked along the length of the borer’s ovipositor, they also 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.
Next, they investigated the material from which the drill bit was made in order to find out what made it so hard. 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,” said Gundiah.
They then prodded the minute drill bit with an atomic force microscope probe to measure how hard the zinc-enriched teeth were, and they found them to be almost as hard as the acrylic cement used for dental implants.
Having characterized the fig wasp’s drill bit, Gundiah is keen to design a minute boring tool based on the lessons she has learned from these insects.
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