Le vol de la libellule - Flight of the dragonfly

Les ingénieurs électriciens de l'Université de Duke ont développé un système de télémétrie sans fil, léger mais assez puissant pour permettre aux scientifiques d'étudier l'activité neurologique complexe des libellules lorsqu'elles capturent leurs proies.
Jusqu'à présent, les études passées sur le comportement des insectes ont été limitées par la difficulté de collecter des données et les méthodes sont trop lourdes pour leur permettre d'agir de manière normale, comme ils le font dans la nature. Le nouveau système n'utilise pas de batteries, mais plutôt envoie le courant par rayon à la libellule qui vole.

 Cordulie bronzée, mâle  en observation

  Cordulia aenea - Cordulidae

 Downy emerald

 

En essayant de mieux comprendre le système de commande du vol complexe des libellules, ces ingénieurs collectent leurs informations en attachant des électrodes minuscules aux cellules nerveuses individuelles dans le système nerveux de la libellule et enregistrant l'activité électrique des neurones de la libellule et des muscles. Des systèmes existants pour enregistrer l'activité neurale exigent des batteries beaucoup trop lourdes pour être portées par une libellule; les expériences ont donc jusqu'à présent été effectuées avec des libellules immobilisées.

 Libellule déprimée, femelle  en ponte 
 Libellula depressa - Libellulidae

 The Broad-bodied Chaser

 

Si le nouveau système s'avère fructueux, les chercheurs s'attendent à ce que de nouvelles et passionnantes possibilités dans le comportement de petits animaux s'ouvrent pour la première fois:

Les chercheurs ont développé un système sans fil qui évite la taille et le poids d'une batterie.

Le système fournirait assez de puissance à la puce attachée à une libellule volante pour qu'il puisse transmettre en temps réel les signaux électriques d'un grand nombre de ses neurones.

Libellule fauve mâle en observation

Libellula fulva - Libellulidae

 Scarce Chaser

 

Le système pourrait envoyer assez d'énergie depuis la puce pour permettre de renvoyer des masses de données à plus de cinq mégabits par seconde, ce qui est comparable à une connexion à Internet privée moyenne. Les scientifiques cherchent à synchroniser les données neuronales et les réunir par le biais de la puce à une vidéo haut débit alors que l'insecte est en  vol.

La puce, avec deux antennes fines comme des cheveux sera fixée sous l'insecte pour ne pas gêner le mouvement de ses ailes, la puce devant avoir un contact radio ininterrompu avec l'émetteur.

Orthetrum réticulé femelle en ponte 

Orthetrum cancellatum - Libellulidae

Black-tailed Skimmer

  

  
Flight of the dragonfly:

Past studies of insect behavior have been limited by the fact that today's remote data collection, or telemetry, systems are too heavy to allow the insects to act naturally, as they would in the wild. The new system uses no batteries, but rather beams power wirelessly to the flying dragonfly.

Duke electrical engineer Matt Reynolds, working with Reid Harrison at Intan Technologies, developed the chip for scientists at the Howard Hughes Medical Institute (HHMI), who are trying to better understand the complex flight control system of dragonflies. They gather their information by attaching tiny electrodes to individual nerve cells in the dragonfly’s nerve cord and recording the electrical activity of the dragonfly's neurons and muscles. Existing systems for recording neural activity require large batteries that are far too heavy to be carried by a dragonfly, so experiments to date have been carried out with immobilized dragonflies.

If the new system proves successful, the researchers expect that broad new avenues into studying behavior of small animals remotely will become available for the first time.

“We developed a wireless power system that avoids the need altogether for the size and weight of a battery,” said Reynolds, assistant professor of electrical and computer engineering at Duke’s Pratt School of Engineering. He presented the results of his work today at the annual Biomedical Circuits and Systems Conference, held by the Institute of Electrical and Electronics Engineers (IEEE) in San Diego.

“The system provides enough power to the chip attached to a flying dragonfly that it can transmit in real time the electrical signals from many dragonfly neurons,” Reynolds said.

The chip receives power wirelessly from a transmitter within the flight arena in which the experiments are carried out. The system can send enough power to the chip to enable it to send back reams of data at over five megabits per second, which is comparable to a typical home internet connection. This is important, the scientists said, because they plan to sync the neuronal data gathered from the chip with high-speed video taken while the insect is in flight and preying on fruit flies.

“Capturing this kind of data in the past has been exceedingly challenging,” said Anthony Leonardo, a neuroscientist who studies the neural basis of insect behavior at HHMI’s Janelia Farm Research Campus in Virginia. “In past studies of insect neurons the animal is alert, but restrained, and observing scenarios on a projection screen. A huge goal for a lot of researchers has been to get data from live animals who are acting naturally.”

The average weight of the dragonfly species involved in these studies is about 400 milligrams, and Leonardo estimates that an individual dragonfly can carry about one-third of its weight without negatively impacting its ability to fly and hunt. Currently, most multi-channel wireless telemetry systems weigh between 75 and 150 times more than a dragonfly, not counting the weight of the battery, which rules them out for most insect studies, he said. A battery-powered version of the insect telemetry system, previously developed by Harrison and Leonardo, weighs 130 milligrams -- liftable by a foraging dragonfly but with difficulty.

The weight of the chip that Reynolds and his team developed is just 38 milligrams, or less than half of a typical postage stamp. It is also one-fifth the weight and has 15 times greater bandwidth of the previous generation system, Reynolds said.

The researchers expect to begin flight experiments with dragonflies over the next few months. The testing will take place in a specially designed flight arena at HHMI's Janelia Farm complex equipped with nature scenes on the walls, a pond and plenty of fruit flies for the dragonflies to eat.

The chip, with two hair-thin antennae projecting from the back, will be attached to the belly of the insect so as not to interfere with the wings. Since the chip must have uninterrupted radio contact with the power transmitter on the ground, the chip is carried much like the backup parachute on the underside of the animal.