Half-moth, half machine, a new generation of remote-controlled insects could one day be used as spies
GOVERNMENT spooks want cyborg insects to snoop on their enemies. Biologists want to tap into the nervous systems of insects to understand how they fly. A probe that can be implanted into moths to control their flight could help satisfy both parties. One day, it could even help rehabilitate people who have had strokes.
The US Defense Advanced Research Projects Agency (DARPA) has been running a programme to develop machine-insect interfaces for years but electrodes implanted to stimulate the brains or wing muscles of insects were not precise enough. Now Joel Voldman of the Massachusetts Institute of Technology and colleagues have designed a unique, flexible neural probe that can be attached directly to an insect's ventral nerve cord (VNC), which, along with the brain, makes up the central nervous system in insects.
Another reason previous attempts have not been entirely successful was because the impedance of the electrodes did not match that of the insect's tissue. This probe is made of a polyimide polymer coated with gold and carbon nanotubes, and its impedance is much closer to that of nerve tissue. One end of the probe is a ring that clamps around the VNC. The inside of the ring has five electrodes which stimulate distinct nerve bundles within the VNC.
Attached to the probe is a wireless stimulator, which contains a radio receiver, as well as a battery and a device to generate electrical pulses. The team implanted the device in the abdomen of a tobacco hawkmoth (Manduca sexta). As it weighs less than half a gram, it is easy for the moth to carry. "Their wingspan is the width of your hand," says Voldman. "These are big guys."
Testing on tethered moths revealed that stimulating one side of the VNC made the moth's abdomen turn one way, and vice versa (Journal of Neuroscience Methods, DOI: 10.1016/j.jneumeth. 2011.11.026). The amount the abdomen turned depended on the strength of the current, which ranged from about 1 to 10 microamperes. The team then implanted the device in untethered moths and sent commands remotely. The moths turned left or right whenever the appropriate signal was delivered (see video at newscientist.com/article/dn21431)
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"This is a major advance," says insect neurobiologist Roy Ritzmann at Case Western Reserve University in Cleveland, Ohio. DARPA hopes this kind of control will one day allow intelligence agencies to use insects to carry surveillance equipment and spy on unsuspecting enemies.
The researchers also found that the relatively low current required to control the moth meant they were able to pick up nerve signals. This should allow them to gain an insight into the impulses that make a moth fly, something that has not been possible with previous electrode designs. The low current was also less damaging to the moth.
Voldman's team is now talking to neurobiologists to see if the probe could be used in humans. "It turns out there are a bunch of cylindrical nerves in humans that are about the same size," says Voldman. Electrodes that stimulate nerve bundles could help rehabilitate people who have lost mobility after a stroke.
So will insect cyborgs soon become a reality? "It is a step toward that goal, but we are still a long way away," says Ritzmann. "To really get to a cyborg, we would need to tap where behavioural commands come from and often that is the brain. We are just starting to understand these brain circuits."
Cy-bugs make their own power
A true cyborg insect needs more than neural circuits. It also needs a power source, and batteries won't cut it over long periods.
Daniel Scherson at Case Western Reserve University in Cleveland, Ohio, and colleagues built a fuel cell that taps into an insect's chemical energy. The fuel cell's anode was coated with two enzymes: the first converts a sugar called trehalose in an insect's blood into glucose; the second oxidised the glucose and extracted electrons.
When implanted into the abdomen of a female cockroach, the fuel cell delivered about 55 microwatts per square centimetre of electrode (Journal of the American Chemical Society, DOI: 10.1021/ja210794c).
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