The Berkeley team implanted electrodes into the brain and muscles of two species: green June beetles called Cotinus texana from the southern US, and the much larger African species Mecynorrhina torquata. Both responded to stimulation in much the same way, but the weight of the electronics and their battery meant that only Mecynorrhina – which can grow to the size of a human palm – was strong enough to fly freely under radio control.
A particular series of electrical pulses to the brain causes the beetle to take off. No further stimulation is needed to maintain the flight. Though the average length of flights during trials was just 45 seconds, one lasted for more than 30 minutes. A single pulse causes a beetle to land again.
The insects' flight can also be directed. Pulses sent to the brain trigger a descent, on average by 60 centimetres. The beetles can be steered by stimulating the wing muscle on the opposite side from the direction they are required to turn, though this works only three-quarters of the time. After each manoeuvre, the beetles quickly right themselves and continue flying parallel to the ground.
Tyson Hedrick, a biomechanist at the University of North Carolina, Chapel Hill, who was not involved in the research, says he is surprised at the level of control achieved, because the controlling impulses were delivered to comparatively large regions of the insect brain.
Precisely stimulating individual neurons or circuits may harness the beetles more precisely, he told New Scientist, but don't expect aerial acrobatics. "It's not entirely clear how much control a beetle has over its own flight," Hedrick says. "If you've ever seen a beetle flying in the wild, they're not the most graceful insects."
The research may be more successful in revealing just how the brain, nerves and muscles of insects coordinate flight and other behaviours than at bringing six-legged cyborg spies into service, Hedrick adds. "It may end up helping biologists more than it will help DARPA."
It's a view echoed by Reid Harrison, an electrical engineer at the University of Utah, Salt Lake City, who has designed brain-recording backpacks for insects. "I'm sceptical about their ability to do surveillance for the following reason: no one has solved the power issue."
Batteries, solar cells and piezoelectrics that harvest energy from movement cannot provide enough power to run electrodes and radio transmitters for very long, Harrison says. "Maybe we'll have some advances in those technologies in the near future, but based on what you can get off the shelf now it's not even close."
Journal reference: Frontiers in Integrative Neuroscience, DOI: 10.3389/neuro.07.024.2009