Wasps, Motherhood and Ultrasound

Female Pimpla wasp locating a moth pupa. © 2014 Beatriz Moisset

A slender wasp lands on a plant stem and starts gently tapping it with the tips of her thread-like long antennae. Tap-tap-tap, she goes up and down the stem. She may abandon her search and repeat the same process on another plant, and another. When she finally finds what she is looking for, the tapping becomes more pronounced and remains concentrated in a single spot. A Pimpla wasp is delicately built, glossy black with bright orange legs. Its body ends in a sword-like projection used for egg laying and called ovipositor. This is how we know she is a female. Her methodical activity is a preparation for motherhood.

At a hospital an expectant mother is having a sonogram of her fetus. The technician gets the equipment ready, applies gel to the mother's belly and runs a wand over it. The image of the baby inside the womb emerges in the monitor. The invisible becomes visible through the magic of ultrasound technology.

Ultrasound of a fetus. By Pacres. Flickr

These two unrelated events have something in common. The expectant wasp mother is also using ultrasound for the benefit of her progeny. The amazing thing is that she and her ancestors have been using this technology for millions of years. Even more amazing is that she carries all the needed equipment in her tiny body. One big difference is that she is not observing her unborn baby but locating the food her baby will need. Other wasps have an easier time. They hunt for caterpillars, which are relatively easy to find because they make noises when munching away. But a pupa remains perfectly still and requires special equipment to be detected.

The ultrasound equipment used to see a fetus inside the mother's womb consists of a machine that produces high-pitch vibrations, beyond human hearing, and a sensor, called a transducer, that collects and interprets the sounds bounced back from the mother's body, her placenta, and the little body curled up inside.

The Pimpla wasp vibrates her body in a special way, producing ultrasound waves which she transmits to the plant surface through her antennae. She absorbs the bounced back ultrasound through her legs where some tiny organs, called subgenual (below the knee) organs , collect information on the shape, size and location of its quarry. An image develops in her minuscule brain, an image similar to the ones we have all seen of unborn babies inside the womb. Now she knows exactly where to lay her egg.

Pimpla wasp, female. © 2014 Beatriz Moisset

She bends her abdomen and points the sharp ovipositor toward the hiding moth pupa. She inserts an egg on it and leaves. Her mission accomplished, she starts looking for other occult cocoons to lay more eggs on them.

We marvel about bats and dolphins using a similar process, echolocation. It is remarkable that a tiny insect can also use a version of this complicated technology.

AGRIS. Vibrational sounding by the pupal parasitoid Pimpla turionellae

REDIA. The Subgenual Organ in Pimpla turionellae

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© Beatriz Moisset. 2014