Cockroach Sensitivity

Cockroaches seem to be able to detect static electricity with their antennae, which are pulled towards an electrical field just as human hairs are pulled towards a balloon that's been charged by being rubbed on a jumper.

Researchers don't think the insects evolved this ability because it helps them survive to pass on their genes; instead, it's a side-effect of having long, thin antennae that can easily be charged and moved around by electrical fields.

"It's not a specialist adaptation," says Dr Chris Jackson, a biologist at the University of Southampton and one of the paper's authors. "It seems we are just talking about the ability of a static electrical field to exert force on a very sensitive sensory organ. The roaches feel as if something is touching their antennae, and this triggers their avoidance response."

The response also works in reverse ñ moving a cockroach's antennae by other means makes it react as if it had encountered static electricity.

The results seem to apply to most insects, and could help researchers develop new methods of pest control.

An insect sixth sense?

The experiments used a Y-shaped tube; researchers put cockroaches into the bottom end of the Y, and monitored their choices of path when they came to the fork, both under normal conditions and when one fork contained a static electrical field.

Without an electrical field, the cockroaches showed no significant preference for one fork over the other. When an electrical field was switched on, they chose the other fork 85 per cent of the time.

Insects with their antennae removed failed to detect electrical fields; preventing the antennae from moving badly harmed this ability, though it did not entirely remove it. Eventually the researchers identified the hair plates at the base of the cockroaches' antennae as the crucial component of their ability to detect static electricity. The team used high-speed video footage to monitor how the cockroaches' antennae moved as they approached an electrical field.

Taking the investigation further presented a conundrum, electrical fields would interfere with instruments designed to detect neuronal activity, so the scientists needed to come up with another way of deflecting the creatures' antennae from their normal position. They settled on covering the antennae with tiny iron particles and using a magnetic field to move them. The cockroaches responded just as if they had encountered a static electrical field, and the team found this caused activity in the insect's nervous system.

This method drew on long-standing links between Southampton scientists and fellow author Professor Masakazu Takahata at Hokkaido University in Japan, who has been using magnetic fields to understand how the gravity receptors of crayfish function. The multidisciplinary research on cockroaches also involved Dr Suleimen Sharkh, an engineer at Southampton University, who provided expertise on setting up the electrical and magnetic fields and who was able to precisely define the strengths of the fields the roaches encountered.

When a cockroach approaches a positively-charged field, the electricity induces an uneven distribution of charge around the insect, with negative charge concentrated around its antennae, the parts of its body that are closest the electrode. Opposite charges attract, so the negatively-charged antennae bend towards the positively-charged electrode.

This antennal movement is picked up, the researchers believe, by the sensitive hair plates at the base of the antennae. These plates also play a major role in the insects' behaviour more widely, and agitating them triggers flight or avoidance behaviour.

Early follow-on work suggests that other organisms like ants, parasitoid wasps and fruit flies all have similar responses to electrical fields. If an insect has an appendage that can flex, an induced charge will flex it and cause the insect to move away. Other insects have been observed to behave differently around electrical fields such as those generated by power cables. Fields from household and office equipment could affect cockroaches' behaviour in similar ways.

Roach control

The results could be significant for the design of future power lines. The UK's national grid is due for redevelopment to cope with the much higher loads being placed on it. When designing replacement power lines, it would be a good idea to bear in mind the possible effects of man-made electrical fields on insect behaviour.

If you have a power line running across your field, and you are a grower using integrated pest management, relying on parasitoids and predators to control pest species, then it could be a real problem if these predators are being deterred and confused by static electricity.

Eventually, electrical charges could be used as a new form of pest control. Though the fields used in the experiment sound impressive at around 2kv, the fact that this is static electricity with no current and insignificant power means it is not dangerous. You would probably get a charge similar to this from walking across a carpet.

This means similar static voltages could safely be used to keep insects out of buildings by surrounding doors or ventilation shafts with an electrical field. This could either be done by an active circuit, or by a lower-tech system, perhaps involving a brush on the bottom of a door that would charge an area of floor whenever the door was opened, preventing insect access.

Article provided by Lavender Pest Control