Fig wasps use a unique tool to find the best place to lay eggs - a tube, called an ovipositor, hardened with zinc. Biologists are amazed at the discovery.
Female insects spend a lot of time and effort trying to find the best place to lay their eggs. Fig wasps, true to their name, deposit their developing young in the fruit of fig plants.
One species of parasitic fig wasp, Apocryta westwoodi grandi, digs into unripe fruit, attempting to find eggs laid by other wasps. When deposits are discovered, the female destroys the eggs, and deposits her own, to provide the best chance for her brood.
The ovipositor of this species is one-third of an inch long, and equipped with a needle-like tip that can dig deep in the tough fruit.
Namrata Gundiah of the Indian Institute of Science in Bangalore set out to examine anatomical differences between this species of fig wasp and varieties that pollinate the flowers of the plant.
"Female insects of diverse orders bore into substrates to deposit their eggs. Such insects must overcome several biomechanical challenges to successfully [lay eggs], which include the selection of suitable substrates through which the ovipositor can penetrate without itself fracturing," researchers wrote in an article, detailing their findings.
Laksminath Kundanati, a graduate student at the school, teamed up with Gundiah for his research. The team examined ovipositors of the fruit-boring species, using electron microscopes. They found tips of the slender probes are designed like drill bits, including teeth to drill through the tough material. Researchers also found small pits in the probe, where it needs to bend during penetration, in order to avoid breaking. The tip was found to feature small sensory organs, allowing the female to guide the probe into a prime laying location.
The ovipositor of the pollinator wasp was shaped more like a spoon.
When the researchers studied the chemical makeup of the ovipositor tip, they found the structure is hardened with zinc. Presence of the metal was detected by targeting a beam of electrons on the tip, which emitted characteristic x-rays, revealing zinc. This element is also used in commercial drill bits, adding hardness to the tool accessories. Kundanati measured the hardness of the tip as being equal to that of dental implants.
"Such studies may be useful for the biomimetic design of surgical tools and in the use of novel mechanisms to bore through hard substrates," researchers stated.
Study of the fig wasps and ovipositors toughened with zinc was detailed in The Journal of Experimental Biology.
