Future surgeries requiring a doctor to dive deep into the body might be made considerably less invasive thanks to an unlikely inspiration: a parasitic fig wasp.
Mechanical engineers at the Indian Institute of Science have been investigating the reproductive process of Apocryta westwoodi grandi, a wasp that deposits its eggs inside a developing fig fruit next to those of another species of wasp. When the eggs hatch, they feed on the larvae of the non-parasitizing wasp before growing and emerging into the world.
While the interactions of the two wasp species and the plant are biologically interesting in their own right, the part that caught the eyes of researchers in Namrata Gundiah’s biomechanics laboratory was how the parasitic wasp deposited its eggs deep within the fruit.
Like many insects and some other animals, the parasitic wasp deposits its eggs through a long tubular organ called an ovipositor. But this particular wasp must pierce the skin and bore through the tough tissue of an unripened fig.
“From a mechanical perspective, it’s really interesting how this insect can penetrate a needle that is really quite flexible into hard material,” doctoral student Lakshminath Kundanati tells Txchnologist. “So we looked at the structure of the needle and whether any parts on it are specifically adapted to help.”
The team, whose findings were published on June 1 in The Journal of Experimental Biology, found a number of interesting parts. The needle anatomy is composed of three parts that slide along each other’s lengths and are connected by rail guides using dovetail joints. These moving parts help the needle pierce and cut tissue.
The front of the ovipositor needle is actually a drill bit, with projecting teeth that are hardened against wear and stiffened by enrichment with the metal zinc. At the same time, the ovipositor tissue behind the bit is embedded with hole-like structures that absorb energy and let the organ bend so it can be steered as it bores.
The wasp stretches and manipulates its abdomen until it resembles nothing as much as an oil derrick tower, a structure built by people to position drills to bore for petroleum.
(initial anchoring of ovipositor at suitable location. Courtesy L. Kundanati/J. Exp. Biol.)
Kundanati says the wasp uses its derrick and body movements to steer its drill through the fruit. Also, one part of the animal’s drill tip is curved, “so when it pushes that one part forward it gets more of an angle and more steering,” he says. “There can be a 20- to 30-degree deflection from the needle’s starting angle to where it ends. That’s quite a lot.”
(Steerability of parasitoid ovipositor in the fig substrate. (A) Tracings showing the curved path taken by the ovipositor in the fig substrate that illustrate maneuvering of the ovipositor inside the substrate. (B) SEM images of the parasitoid ovipositor showing the dorsal and ventral valves that comprise the ovipositor. The inset shows a possible mechanical stopper sensillum, indicated by the white arrow, which may be useful in limiting displacement between the two ovipositor parts. Courtesy L. Kundanati/J. Exp. Biol.)
Finally, the scientists found that chemical and mechanical sensors at the bit and along the ovipositor send back environmental information. The insect uses this data to home in on another wasp’s eggs so it can precisely deposit its own.
The whole process from inserting the needle into the fig to depositing eggs and removing the organ can take five to 10 minutes. This is a lot of time to remain immobilized in a hungry world, as shown in this gif:
(Ant predation while wasp’s ovipositor is inserted in fig. Courtesy L. Kundanati/J. Exp. Biol.)
“Obviously, the key challenge for this wasp is that it has to remove the needle when a predator comes,” he says. “That doesn’t always happen fast enough.”
Even though more research into the biomechanics and material composition of the organ need to be done, the researchers think that there is promise in using some of the wasp’s adaptations to make better medical technology.
“The most interesting part of how this insect works is the mechanical combination of hardening and flexibility,” he says. “If we could develop this, we could make very small, minimally invasive tools that could, for example, navigate around parts of the brain you want to avoid or through arteries to perform surgeries.”
Top gif: Parasitic fig wasp drills into fig fruit with zinc-hardened ovipositor. Courtesy L. Kundanati/J. Exp. Biol.
