Insects all charged up to deliver a lethal blow

When an insect walks across a surface, it generates minute electrical charges which are being harnessed by scientists at the University of Southampton in a bid to build an eco-friendly pest control device which would reduce the need for indiscriminate use of insecticides. Dr Chris Jackson and Daniel McGonigle of the University's Biodiversity and Ecology Research Division describe their hopes for their electrostatic flytrap in this week's New Scientist magazine.

The researchers have found that the process at work when you rub a balloon on a sweater to charge it up with static electricity, or receive a shock after walking on certain types of carpet, can also affect insects such as houseflies. The process - triboelectrification - results in the house fly becoming positively charged as it walks across some types of plastics.

Dr Jackson explains how this can then be used in pest control. "A charged body - even a fly - will attract objects of the opposite charge, including particles carrying insect diseases," he says. "A fly will enter the trap, and on contact with the surface become positively charged. It is then exposed to negatively charged particles that will stick to the fly's body. Initially we are using naturally occurring biocontrol agents that can cause a lethal disease in flies, but will not be passed on to other insects or to people."

Daniel McGonigle adds, "A negatively charged powder containing the spores of a fungus, Metarhizium anisopliae, will be picked up by the flies entering the trap. These infected flies will spread the fungus to other flies in the week or so before they die, so the fungus will be effective at controlling the insects where needed, but it won't have the indiscriminate effect that some pesticides have."

The researchers hope to test out the first housefly prototypes this summer. "They will probably be more acceptable for the agricultural sector than the domestic market," comments Dr Jackson.

As part of their research, Dr Jackson and Daniel McGonigle developed a model to explain the electrostatic charging of walking insects, with different plastic surfaces inducing different charges. Working with John Davidson of the University's Electronics and Computer Science Department, they have also shown that the flies leave behind a small electrical 'footprint' of the reverse polarity on the surface.

The use of electrostatics for pest control has a wide range of applications, some of which are already being exploited by ExoSect Ltd, a University of Southampton spin-off company based at the Chilworth Science Park.